use "branch-20" for memcached, and "master" for libconflate

Change-Id: Idec45a49f121d757ee63bf2f1e5bc5149261e36e
Reviewed-on: http://review.couchbase.org/26876
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>