CBQE-1338 Allow install.py to install couchbase on MAC

Change-Id: I259f490e0a57733a07bafad23bee99a5d01ef32f
Reviewed-on: http://review.couchbase.org/27270
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>
Tested-by: Chisheng Hong <chisheng@couchbase.com>