Add support for ProxyCommand in GerritSSHClient
Add support for ProxyCommand in GerritSSHClient

Change-Id: I776a58b2cdac17e3eafc985ee727cd88e8294ccc

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