MB-9581: Use couchdb 2.1.1 branch

In the 2.5.0 manifest the couchdb component shouldn't (yet) be
pinnend to a specific commit, but to the working branch which
is 2.1.1.

Change-Id: I0937bb541152db77a099f0223dd74f74488d8da1
Reviewed-on: http://review.couchbase.org/30384
Tested-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Philip Labee <philip@couchbase.com>