Fix xml request doesn't work with unicode

Fix bug 1160704

* httplib2 doesn't work with unicode url and params. So encode all unicode
to utf-8 before request.
* Fix xml serializer doesn't work with unicode
* Decode command argument to unicode in main function
* Exception's message maybe include unicode, decode message to unicode
before logging or print.
* Sync the changing of serializer/deserilizer's code with quantum server code
  https://review.openstack.org/#/c/25482/
  https://review.openstack.org/#/c/25046/
  https://review.openstack.org/#/c/21410/
* Enable xml test

Change-Id: Ib140e34d54cc916e2ea172e4bad9e4a77388723a
Merge "Fix xml request doesn't work with unicode"