Fix updated timestamp for SecurityGroup model

Reasons:
 - Security group "updated" timestamp is not being
   updated when new rule appears. It still the same as "created".
 - Security group "updated" timestamp is not being
   updated when rule is being deleted.

Changes:
 - adding `save` step after security group rules creation.
 - adding `save` step after security group rules deletion.
 - adding integration test that validates that timestamp
   was changed after creation and deletion.

Change-Id: I92ee7207366511cd4bc5dff07337031faeed0182
Closes-Bug: #1325967
Merge "Fix updated timestamp for SecurityGroup model"