[SPARK-24131][PYSPARK] Add majorMinorVersion API to PySpark for determining Spark versions

## What changes were proposed in this pull request?

We need to determine Spark major and minor versions in PySpark. We can add a `majorMinorVersion` API to PySpark which is similar to the Scala API in `VersionUtils.majorMinorVersion`.

## How was this patch tested?

Added tests.

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes #21203 from viirya/SPARK-24131.

python/pyspark/util.py

@@ -16,6 +16,7 @@
 # limitations under the License.
 #
 
+import re
 import sys
 import inspect
 from py4j.protocol import Py4JJavaError
@@ -61,6 +62,26 @@ def _get_argspec(f):
     return argspec
 
 
+def majorMinorVersion(version):
+    """
+    Get major and minor version numbers for given Spark version string.
+
+    >>> version = "2.4.0"
+    >>> majorMinorVersion(version)
+    (2, 4)
+
+    >>> version = "abc"
+    >>> majorMinorVersion(version) is None
+    True
+
+    """
+    m = re.search('^(\d+)\.(\d+)(\..*)?$', version)
+    if m is None:
+        return None
+    else:
+        return (int(m.group(1)), int(m.group(2)))
+
+
 if __name__ == "__main__":
     import doctest
     (failure_count, test_count) = doctest.testmod()