Get Gerrit version during client initialisation
Get Gerrit version during client initialisation

Later the client might have functionality that only works on
certain versions of Gerrit.  Store the Gerrit version during
initialisation.

Change-Id: Idcd35baf00d6cd583f6f85b68c4b0a0c3653344b

morucci/pygerrit,sonyxperiadev/pygerrit,dpursehouse/pygerrit2,markon/pygerrit2,dpursehouse/pygerrit,gferon/pygerrit2,benjiii/pygerrit