Fix security group race condition while creating rule

Previously, it was possible for someone to create a security group rule
where the rule references another security group. To do this nova would
first create the security group rule and then look up the referenced group
(group_id's) name in order to return that via the api. During this time
it's possible for someone to delete this security group rule and the
referenced group before the call returned resulting in a 404 error being
raised. This patch addresses this issue by looking up the group name
first and then creating the security group rule in order to avoid this
from occuring.

Note: this patch also adds a test to cover the case where an invalid group
id was passed though this does not really add any real additional coverage
to the change largely because the code is currently using global stubs. That
said, the previous coverage should hopefully be sufficient

Change-Id: If58ffa5629ba5166f260379ac47922974de31be0
Related-bug: 1262566
Merge "Fix security group race condition while creating rule"