[SPARK-3405] add subnet-id and vpc-id options to spark_ec2.py

Based on this gist:
https://gist.github.com/amar-analytx/0b62543621e1f246c0a2

We use security group ids instead of security group to get around this issue:
https://github.com/boto/boto/issues/350

Author: Mike Jennings <mvj101@gmail.com>
Author: Mike Jennings <mvj@google.com>

Closes #2872 from mvj101/SPARK-3405 and squashes the following commits:

be9cb43 [Mike Jennings] `pep8 spark_ec2.py` runs cleanly.
4dc6756 [Mike Jennings] Remove duplicate comment
731d94c [Mike Jennings] Update for code review.
ad90a36 [Mike Jennings] Merge branch 'master' of https://github.com/apache/spark into SPARK-3405
1ebffa1 [Mike Jennings] Merge branch 'master' into SPARK-3405
52aaeec [Mike Jennings] [SPARK-3405] add subnet-id and vpc-id options to spark_ec2.py