[SPARK-5469] restructure pyspark.sql into multiple files

All the DataTypes moved into pyspark.sql.types

The changes can be tracked by `--find-copies-harder -M25`
```
davieslocalhost:~/work/spark/python$ git diff --find-copies-harder -M25 --numstat master..
2       5       python/docs/pyspark.ml.rst
0       3       python/docs/pyspark.mllib.rst
10      2       python/docs/pyspark.sql.rst
1       1       python/pyspark/mllib/linalg.py
21      14      python/pyspark/{mllib => sql}/__init__.py
14      2108    python/pyspark/{sql.py => sql/context.py}
10      1772    python/pyspark/{sql.py => sql/dataframe.py}
7       6       python/pyspark/{sql_tests.py => sql/tests.py}
8       1465    python/pyspark/{sql.py => sql/types.py}
4       2       python/run-tests
1       1       sql/core/src/main/scala/org/apache/spark/sql/test/ExamplePointUDT.scala
```

Also `git blame -C -C python/pyspark/sql/context.py` to track the history.

Author: Davies Liu <davies@databricks.com>

Closes #4479 from davies/sql and squashes the following commits:

1b5f0a5 [Davies Liu] Merge branch 'master' of github.com:apache/spark into sql
2b2b983 [Davies Liu] restructure pyspark.sql

1 files changed, 4 insertions, 2 deletions

diff --git a/python/run-tests b/python/run-tests
index 649a2c44d1..58a26dd8ff 100755
--- a/python/run-tests
+++ b/python/run-tests
@@ -64,8 +64,10 @@ function run_core_tests() {
 
 function run_sql_tests() {
     echo "Run sql tests ..."
-    run_test "pyspark/sql.py"
-    run_test "pyspark/sql_tests.py"
+    run_test "pyspark/sql/types.py"
+    run_test "pyspark/sql/context.py"
+    run_test "pyspark/sql/dataframe.py"
+    run_test "pyspark/sql/tests.py"
 }
 
 function run_mllib_tests() {