[SPARK-8603][SPARKR] Use shell() instead of system2() for SparkR on Windows

## What changes were proposed in this pull request?

This PR corrects SparkR to use `shell()` instead of `system2()` on Windows.

Using `system2(...)` on Windows does not process windows file separator `\`. `shell(tralsate = TRUE, ...)` can treat this problem. So, this was changed to be chosen according to OS.

Existing tests were failed on Windows due to this problem. For example, those were failed.

  ```
8. Failure: sparkJars tag in SparkContext (test_includeJAR.R#34)
9. Failure: sparkJars tag in SparkContext (test_includeJAR.R#36)
```

The cases above were due to using of `system2`.

In addition, this PR also fixes some tests failed on Windows.

  ```
5. Failure: sparkJars sparkPackages as comma-separated strings (test_context.R#128)
6. Failure: sparkJars sparkPackages as comma-separated strings (test_context.R#131)
7. Failure: sparkJars sparkPackages as comma-separated strings (test_context.R#134)
```

  The cases above were due to a weird behaviour of `normalizePath()`. On Linux, if the path does not exist, it just prints out the input but it prints out including the current path on Windows.

  ```r
# On Linus
path <- normalizePath("aa")
print(path)
[1] "aa"

# On Windows
path <- normalizePath("aa")
print(path)
[1] "C:\\Users\\aa"
```

## How was this patch tested?

Jenkins tests and manually tested in a Window machine as below:

Here is the [stdout](https://gist.github.com/HyukjinKwon/4bf35184f3a30f3bce987a58ec2bbbab) of testing.

Closes #7025

Author: hyukjinkwon <gurwls223@gmail.com>
Author: Hyukjin Kwon <gurwls223@gmail.com>
Author: Prakash PC <prakash.chinnu@gmail.com>

Closes #13165 from HyukjinKwon/pr/7025.

3 files changed, 32 insertions, 7 deletions

diff --git a/R/pkg/inst/tests/testthat/test_Windows.R b/R/pkg/inst/tests/testthat/test_Windows.R
new file mode 100644
index 0000000000..8813e18a1f
--- /dev/null
+++ b/R/pkg/inst/tests/testthat/test_Windows.R
@@ -0,0 +1,26 @@
+#
+# 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.
+#
+context("Windows-specific tests")
+
+test_that("sparkJars tag in SparkContext", {
+  if (.Platform$OS.type != "windows") {
+    skip("This test is only for Windows, skipped")
+  }
+  testOutput <- launchScript("ECHO", "a/b/c", capture = TRUE)
+  abcPath <- testOutput[1]
+  expect_equal(abcPath, "a\\b\\c")
+})
diff --git a/R/pkg/inst/tests/testthat/test_context.R b/R/pkg/inst/tests/testthat/test_context.R
index c1f1a8932d..15915e2d13 100644
--- a/R/pkg/inst/tests/testthat/test_context.R
+++ b/R/pkg/inst/tests/testthat/test_context.R
@@ -129,13 +129,13 @@ test_that("getClientModeSparkSubmitOpts() returns spark-submit args from whiteli
 test_that("sparkJars sparkPackages as comma-separated strings", {
   expect_warning(processSparkJars(" a, b "))
   jars <- suppressWarnings(processSparkJars(" a, b "))
-  expect_equal(jars, c("a", "b"))
+  expect_equal(lapply(jars, basename), list("a", "b"))
 
   jars <- suppressWarnings(processSparkJars(" abc ,, def "))
-  expect_equal(jars, c("abc", "def"))
+  expect_equal(lapply(jars, basename), list("abc", "def"))
 
   jars <- suppressWarnings(processSparkJars(c(" abc ,, def ", "", "xyz", " ", "a,b")))
-  expect_equal(jars, c("abc", "def", "xyz", "a", "b"))
+  expect_equal(lapply(jars, basename), list("abc", "def", "xyz", "a", "b"))
 
   p <- processSparkPackages(c("ghi", "lmn"))
   expect_equal(p, c("ghi", "lmn"))
diff --git a/R/pkg/inst/tests/testthat/test_includeJAR.R b/R/pkg/inst/tests/testthat/test_includeJAR.R
index f89aa8e507..512dd39cb2 100644
--- a/R/pkg/inst/tests/testthat/test_includeJAR.R
+++ b/R/pkg/inst/tests/testthat/test_includeJAR.R
@@ -21,10 +21,9 @@ runScript <- function() {
   sparkTestJarPath <- "R/lib/SparkR/test_support/sparktestjar_2.10-1.0.jar"
   jarPath <- paste("--jars", shQuote(file.path(sparkHome, sparkTestJarPath)))
   scriptPath <- file.path(sparkHome, "R/lib/SparkR/tests/testthat/jarTest.R")
-  submitPath <- file.path(sparkHome, "bin/spark-submit")
-  res <- system2(command = submitPath,
-                 args = c(jarPath, scriptPath),
-                 stdout = TRUE)
+  submitPath <- file.path(sparkHome, paste("bin/", determineSparkSubmitBin(), sep = ""))
+  combinedArgs <- paste(jarPath, scriptPath, sep = " ")
+  res <- launchScript(submitPath, combinedArgs, capture = TRUE)
   tail(res, 2)
 }