Packstack Installer for Grizzly should have a 'exclude-server' option

Issue

• We would like to see this upstream feature merged and be available as a Bug Fix to RHEL 6.4 with Openstack Grizzly.

• This would be a great addition to RHEL because it will allow us to add new servers to an OpenStack cluster. Currently we have to destroy the current cluster and re-intialize it with the new node.

• We tried to add a new nova compute node to the environment by adding the server information to packstack answer file. But upon rerunning packstack with modified answer file, it complains that the private network already exists and eventually fails to add new compute node.

• As a workaround we need to add a dummy network in the answer file and then remove it later. This is not a feasible solution.