Follow up for I0c7e9a28876a1d4278fb2ed8555c2b08472864b9 which added a
ironic_enable_keystone_integration variable to support Ironic in
multi-region environments. This change skips Keystone service
registration based on ironic_enable_keystone_integration rather than
enable_keystone. It also updates the ironic-inspector.conf template to
use the new variable.

Change-Id: I2ecba4999e194766258ac5beed62877d43829313