Simplify add_stream_for_consumer()
Simplify add_stream_for_consumer()

Move the repeated calls to dcp->step() and checking the results into a
lambda.

Change-Id: I3fc90aaff071a6671054288e4c5457a82e276b8d
Reviewed-on: http://review.couchbase.org/104760
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Richard de Mellow <3b8534f7ae49c77465cd6f1b512f27ec39f3eddd@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine