Refactor away the flags.DEFINE_* helpers

The next obvious step in porting to cfg is to define all options using
cfg schemas directly rather than using the flags.DEFINE_* helpers.

This is a large change, but it is almost entirely pure refactoring and
does not result in any functional changes.

The only change to note is that the default values for glance_host,
glance_api_servers and default_publisher_id options are now using opt
value interpolation i.e.

 -glance_host=_get_my_ip()
 +glance_host='$my_ip'

 -glance_api_servers=['%s:%d' % (FLAGS.glance_host, FLAGS.glance_port)]
 +glance_api_servers=['$glance_host:$glance_port']

 -default_publisher_id=FLAGS.host
 +default_publisher_id='$host'

Also note that the lower_bound check on the {report,periodic}_interval
options are no more, but this has been true since cfg was first added.

Change-Id: Ia58c8f0aaf61628bb55b1b8485118a2a9852ed17

nova/objectstore/s3server.py

@@ -44,15 +44,20 @@ import urllib
 import routes
 import webob
 
+from nova.common import cfg
 from nova import flags
 from nova import log as logging
 from nova import utils
 from nova import wsgi
 
 
+buckets_path_opt = \
+    cfg.StrOpt('buckets_path',
+               default='$state_path/buckets',
+               help='path to s3 buckets')
+
 FLAGS = flags.FLAGS
-flags.DEFINE_string('buckets_path', '$state_path/buckets',
-                    'path to s3 buckets')
+FLAGS.add_option(buckets_path_opt)
 
 
 def get_wsgi_server():