Adds barbican keymgr wrapper

Adds barbican keymgr wrapper

Adds a barbican keymgr wrapper to the key manager interface in
cinder.  This allows barbican to be configured as the key manager
for encryption keys in cinder.  The wrapper translates calls from
the existing key manager interface to python-barbicanclient.

There are two new configuration variables: encryption_auth_url
(the authentication URL for the encryption service) and
encryption_api_url (the api URL for the encryption service).

Change-Id: Ifd0d9b073d7f1c3c92d318c20a080b253008b50c
Implements: blueprint encryption-with-barbican
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