Added documentation to keystone.common.dependency.
Added documentation to keystone.common.dependency.

All public attributes now have docstrings describing their interface,
and the module has a top level docstring as well. Previously,
documentation was very sparse.

Closes-Bug: #1252428
Change-Id: I9c83883a6d9ae3201c9037c979689cb82c232120

mahak/keystone,ging/keystone,dsiddharth/access-keys,rushiagr/keystone,reeshupatel/demo,takeshineshiro/keystone,mahak/keystone,JioCloud/keystone,jumpstarter-io/keystone,rushiagr/keystone,openstack/keystone,maestro-hybrid-cloud/keystone,derekchiang/keystone,idjaw/keystone,blueboxgroup/keystone,MaheshIBM/keystone,mahak/keystone,takeshineshiro/keystone,rajalokan/keystone,rushiagr/keystone,rodrigods/keystone,rajalokan/keystone,MaheshIBM/keystone,vivekdhayaal/keystone,vivekdhayaal/keystone,dsiddharth/access-keys,dstanek/keystone,UTSA-ICS/keystone-kerberos,ajayaa/keystone,idjaw/keystone,reeshupatel/demo,dstanek/keystone,rajalokan/keystone,UTSA-ICS/keystone-kerberos,ilay09/keystone,openstack/keystone,jumpstarter-io/keystone,klmitch/keystone,ilay09/keystone,cernops/keystone,ging/keystone,jonnary/keystone,himanshu-setia/keystone,dims/keystone,himanshu-setia/keystone,ilay09/keystone,vivekdhayaal/keystone,openstack/keystone,promptworks/keystone,klmitch/keystone,nuxeh/keystone,cernops/keystone,promptworks/keystone,roopali8/keystone,dims/keystone,derekchiang/keystone,derekchiang/keystone,promptworks/keystone,maestro-hybrid-cloud/keystone,dstanek/keystone,nuxeh/keystone,rodrigods/keystone,jumpstarter-io/keystone,jamielennox/keystone,jamielennox/keystone,blueboxgroup/keystone,nuxeh/keystone,dsiddharth/access-keys,jonnary/keystone,reeshupatel/demo,JioCloud/keystone,roopali8/keystone,ajayaa/keystone