CBQE-1338 Fix bug in cbdocloader automation for MAC

Change-Id: I2dd9e8d7ba39f76265bd34e6d377e2a13324bf88
Reviewed-on: http://review.couchbase.org/26896
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>
Tested-by: Chisheng Hong <chisheng@couchbase.com>