SPY-148: Do not rename the worker thread for listeners.

It's more explicit if the naming of the threads is left to the
executor service (through custom thread factory).

Change-Id: I7457d036b70ba6dd30d6d99dd9d8cbcbaa0cf3dd
Reviewed-on: http://review.couchbase.org/31715
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>