upgrade to pylibcouchbase 1.2.0

Change-Id: Ib7c9422c44ad7dbff134a1d927306db7b3974e62
Reviewed-on: http://review.couchbase.org/32345
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>