Update common apiclient from Oslo

Updated openstack.common.apiclient code from oslo-incubator to commit
8630a44d64c92a0d479e4652bf5ba2cd22416eae

List of changes:

9f1e7eb Correct docstring in load_plugin_from_args
0c4d2c7 Removed set_loaded() method from Resource class
3b248dd Add to_dict() method to apiclient Resource
be81d6b Cleanup unused log related code
8575d87 Removed copyright from empty files
bbaf317 Use encode() instead of strutils.safe_encode() in fake_client
41dc2b4 Encode response from FakeHTTPClient

Removed Resource class from client's code - we should use Resource from
common code.

Change-Id: I0b90999e7832f3796201e40f7df4de7148b832fa
Merge "Update common apiclient from Oslo"