[SPARK-7497] [PYSPARK] [STREAMING] fix streaming flaky tests

Increase the duration and timeout in streaming python tests.

Author: Davies Liu <davies@databricks.com>

Closes #6239 from davies/flaky_tests and squashes the following commits:

d6aee8f [Davies Liu] fix window tests
26317f7 [Davies Liu] Merge branch 'master' of github.com:apache/spark into flaky_tests
7947db6 [Davies Liu] fix streaming flaky tests