Allow storage url override for both auth vers.

When --os-storage-url is specified on the command-line to bin/swift, it
will override the used storage URL regardless of authentication for both
authentication version 1 and version 2.  This can be used to bypass a
load-balancer to hit a specific proxy server for testing/debugging
purposes.

Within the client library, this feature is accessed by passing the
desired storage URL into swiftclient.client.Conection.__init__() via the
os_options keyword argument.  For example:

  conn = Connection(auth_url, user, key, os_options={
    'object_storage_url': 'http://overridden.storage.url/AUTH_foo'})

This patch also adds a dependency on mock>=0.8.0, which is the same as
openstack/swift.

Change-Id: Id2a36ed6abffd65e7762b6beea5bbfc6c036e848
Merge "Allow storage url override for both auth vers."