Refactor: don't use single letter variable

Makes it harder to search for.

Change-Id: I66f704db03d9c45cb96333e32c3c68b34f09a407
Reviewed-on: http://review.couchbase.org/42608
Reviewed-by: Daniel Owen <owend@couchbase.com>
Tested-by: buildbot <build@couchbase.com>