We don't need python cryptography bindings in order to deploy a Galera
server therefore drop it from our dependencies. It also is no longer
used inside OpenStack world for lack of security.
Also, we make remote network hits to get the GPG keys which are quite
unreliable so let's store them inside the role and use them.
Change-Id: I9443f10e8c803599cbebfc2a53cb9c432bfa60d1
c41b80cee9