Add copyright text to glance/openstack/common/__init__.py

Synchronize the content of glance/openstack/common/__init__.py to the
one in oslo-incubator.

Change-Id: Idd059e3f4d00d91c9a14cf302fd780044929e3e5
Closes-bug: #1288877
Merge "Add copyright text to glance/openstack/common/__init__.py"