use better names for "singe" and "multi" tasks

Change-Id: If02b38b3baeb0a03441c66c4e0cd4f2b0dba9700
Reviewed-on: http://review.couchbase.org/24329
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>