Swift doesn't have hard dependency on keystone authentication. Hence
keystonemiddleware is not listed in Keystone's requirements.txt. For
Kolla setup, since keystone is by default enabled, ensure
keystonemiddleware is correctly installed in proxy server Dockerfile.

Change-Id: Ie49433772d7ebe13b984dc0eb93840e6ca54a91a
Closes-Bug: #1537407