Reworked scenario tests to use their own non-default security groups

Moved _create_security_group_nova to base OfficialClientTest class, so
that now it can be used by all scenario tests. All scenario tests now
create security group with "loginable" rules explicitly and attach it to
servers instead of using "default" security group.

Change-Id: If82c681b4a7f62808f46b03c57d113f8f5c97f6f
Closes-Bug: #1247060
Merge "Reworked scenario tests to use their own non-default security groups"