Neutron LBaaS leaking admin_password into logs

Current code leaks the keystone admin_password in the cfg
into log files.

Example from DevStack q-svc.log:
service_auth.admin_password    = password

Issue is that the cfg.StrOpt for admin_password did not set
'secret=True", which would give:
service_auth.admin_password    = ****

Change-Id: I24410641ad48b2e86984b383b144e29478a94344
Closes-Bug: #1549547

neutron_lbaas/common/keystone.py

@@ -43,6 +43,7 @@ OPTS = [
     ),
     cfg.StrOpt(
         'admin_password',
+        secret=True,
         default='password',
         help=_('The service admin password'),
     ),