MB-12913: Use git 1.8.4 from devtools for Centos-65

Use prepackaged git 1.8.4 from the devtools repository instead of
compiling our own.

Change-Id: I9881747782edac3cf4a535d8d549e62f211b6e65
Reviewed-on: http://review.couchbase.org/44466
Tested-by: Dave Rigby <daver@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>