CBQE-1119: implementation execute_couchbase_cli

Change-Id: I384701a5ad7a006b14c7a5222841e34fe7517846
Reviewed-on: http://review.couchbase.org/25309
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>