MB-8083: check if git installed on vms

Change-Id: Icd4188b0493afcabcc63ad74969ad27e91047930
Reviewed-on: http://review.couchbase.org/37649
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>