Fixes errors when nova is disabled

This patch checks if nova is disabled in some
plugins so we can run packstack with
CONFIG_NOVA_INSTALL=n

Fixes: rhbz#1024564

Conflicts:
	packstack/plugins/ceilometer_800.py
	packstack/plugins/cinder_250.py
	packstack/plugins/glance_200.py
	packstack/plugins/mysql_001.py
	packstack/plugins/qpid_002.py
	packstack/plugins/quantum_350.py
	packstack/plugins/swift_600.py
	packstack/puppet/templates/firewall.pp

Change-Id: I05a9bd55c89d4009e28307248d74624533d47240
(cherry picked from commit 768ee0d856174f5019ad3eb127fa836514b738c4)