group to server
In AddServerSecurityGroup, we currently pass the security group
name to novaclient. If multiple security groups with same name
exist, then even while passing secuity group using id to
command 'openstack server add security group <server> <group>'
it results in error 'Multiple security_group matches found'.
Added unit test case to test the command.
Change-Id: I6097eb36e1545c85209cfd767c477e10f82c6999
Closes-Bug: 1604076