Updated openstack/openstack
Project: openstack/keystone  4fb54b32746d4bd0a0b3877205a3dcfa5a5f6745
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Update kvs assignment backend docs

The "key to data" mapping was not documented for the KVS
assignment backend.

Change-Id: Id3cf3e0d9b52ceae5099e6d3833cc88f7aa0f347