Use api_extensions to decide security_group type nova used

Even the system enables neutron, if neutron's security_group
extension is disabled, Nova can still use nova's security_group
by setting security_group_api=nova in nova.conf. So this is to
use neutron's security group only when neutron is enabled and
neutron's security_group extension is enabled.

Change-Id: Id23fdb8cd47fb0ecf0ad0b055dcbb423ff23a239
1 file changed