Adding environment path for XDCR to use TAP : XDCR_USE_OLD_PATH

Change-Id: I618895473bde0f8d576177fdb3a16402a34b9cb4
Reviewed-on: http://review.couchbase.org/35572
Reviewed-by: Tommie McAfee <tommie@couchbase.com>
Tested-by: Aruna Piravi <aruna@couchbase.com>