[SPARK-17663][CORE] SchedulableBuilder should handle invalid data access via scheduler.allocation.file

## What changes were proposed in this pull request?

If `spark.scheduler.allocation.file` has invalid `minShare` or/and `weight` values, these cause :
- `NumberFormatException` due to `toInt` function
- `SparkContext` can not be initialized.
- It does not show meaningful error message to user.

In a nutshell, this functionality can be more robust by selecting one of the following flows :

**1-** Currently, if `schedulingMode` has an invalid value, a warning message is logged and default value is set as `FIFO`. Same pattern can be used for `minShare`(default: 0) and `weight`(default: 1) as well
**2-** Meaningful error message can be shown to the user for all invalid cases.

PR offers :
- `schedulingMode` handles just empty values. It also needs to be supported for **whitespace**, **non-uppercase**(fair, FaIr etc...) or `SchedulingMode.NONE` cases by setting default value(`FIFO`)
- `minShare` and `weight` handle just empty values. They also need to be supported for **non-integer** cases by setting default values.
- Some refactoring of `PoolSuite`.

**Code to Reproduce :**

```
val conf = new SparkConf().setAppName("spark-fairscheduler").setMaster("local")
conf.set("spark.scheduler.mode", "FAIR")
conf.set("spark.scheduler.allocation.file", "src/main/resources/fairscheduler-invalid-data.xml")
val sc = new SparkContext(conf)
```

**fairscheduler-invalid-data.xml :**

```
<allocations>
    <pool name="production">
        <schedulingMode>FIFO</schedulingMode>
        <weight>invalid_weight</weight>
        <minShare>2</minShare>
    </pool>
</allocations>
```

**Stacktrace :**

```
Exception in thread "main" java.lang.NumberFormatException: For input string: "invalid_weight"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:580)
    at java.lang.Integer.parseInt(Integer.java:615)
    at scala.collection.immutable.StringLike$class.toInt(StringLike.scala:272)
    at scala.collection.immutable.StringOps.toInt(StringOps.scala:29)
    at org.apache.spark.scheduler.FairSchedulableBuilder$$anonfun$org$apache$spark$scheduler$FairSchedulableBuilder$$buildFairSchedulerPool$1.apply(SchedulableBuilder.scala:127)
    at org.apache.spark.scheduler.FairSchedulableBuilder$$anonfun$org$apache$spark$scheduler$FairSchedulableBuilder$$buildFairSchedulerPool$1.apply(SchedulableBuilder.scala:102)
```
## How was this patch tested?

Added Unit Test Case.

Author: erenavsarogullari <erenavsarogullari@gmail.com>

Closes #15237 from erenavsarogullari/SPARK-17663.

1 files changed, 80 insertions, 0 deletions

diff --git a/core/src/test/resources/fairscheduler-with-invalid-data.xml b/core/src/test/resources/fairscheduler-with-invalid-data.xml
new file mode 100644
index 0000000000..a4d8d07b67
--- /dev/null
+++ b/core/src/test/resources/fairscheduler-with-invalid-data.xml
@@ -0,0 +1,80 @@
+<?xml version="1.0"?>
+<!--
+  ~ Licensed to the Apache Software Foundation (ASF) under one or more
+  ~ contributor license agreements.  See the NOTICE file distributed with
+  ~ this work for additional information regarding copyright ownership.
+  ~ The ASF licenses this file to You under the Apache License, Version 2.0
+  ~ (the "License"); you may not use this file except in compliance with
+  ~ the License.  You may obtain a copy of the License at
+  ~
+  ~    http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  -->
+
+<allocations>
+   <pool name="pool_with_invalid_min_share">
+        <minShare>INVALID_MIN_SHARE</minShare>
+        <weight>2</weight>
+        <schedulingMode>FAIR</schedulingMode>
+    </pool>
+    <pool name="pool_with_invalid_weight">
+        <minShare>1</minShare>
+        <weight>INVALID_WEIGHT</weight>
+        <schedulingMode>FAIR</schedulingMode>
+    </pool>
+    <pool name="pool_with_invalid_scheduling_mode">
+        <minShare>3</minShare>
+        <weight>2</weight>
+        <schedulingMode>INVALID_SCHEDULING_MODE</schedulingMode>
+    </pool>
+    <pool name="pool_with_non_uppercase_scheduling_mode">
+        <minShare>2</minShare>
+        <weight>1</weight>
+        <schedulingMode>fair</schedulingMode>
+    </pool>
+    <pool name="pool_with_NONE_scheduling_mode">
+        <minShare>1</minShare>
+        <weight>2</weight>
+        <schedulingMode>NONE</schedulingMode>
+    </pool>
+    <pool name="pool_with_whitespace_min_share">
+        <minShare>  </minShare>
+        <weight>2</weight>
+        <schedulingMode>FAIR</schedulingMode>
+    </pool>
+    <pool name="pool_with_whitespace_weight">
+        <minShare>1</minShare>
+        <weight>  </weight>
+        <schedulingMode>FAIR</schedulingMode>
+    </pool>
+    <pool name="pool_with_whitespace_scheduling_mode">
+        <minShare>3</minShare>
+        <weight>2</weight>
+        <schedulingMode>  </schedulingMode>
+    </pool>
+    <pool name="pool_with_empty_min_share">
+        <minShare></minShare>
+        <weight>3</weight>
+        <schedulingMode>FAIR</schedulingMode>
+    </pool>
+    <pool name="pool_with_empty_weight">
+        <minShare>2</minShare>
+        <weight></weight>
+        <schedulingMode>FAIR</schedulingMode>
+    </pool>
+    <pool name="pool_with_empty_scheduling_mode">
+        <minShare>2</minShare>
+        <weight>2</weight>
+        <schedulingMode></schedulingMode>
+    </pool>
+    <pool name="pool_with_surrounded_whitespace">
+        <minShare> 3 </minShare>
+        <weight> 2 </weight>
+        <schedulingMode> FAIR </schedulingMode>
+    </pool>
+</allocations>