Fix: re is not imported.

If re module is not import following error will occured.
poller-debug.log:error: uncaptured python exception, closing channel
<booster-nrpe.NRPEAsyncClient connected at 0x35d64d0> (<type
'exceptions.NameError'>:global name 're' is not defined
[/usr/lib/python2.6/asyncore.py|readwrite|103]
[/usr/lib/python2.6/asyncore.py|handle_read_event|428]
[/var/lib/shinken/modules/booster-nrpe/module.py|handle_read|266]
[/var/lib/shinken/modules/booster-nrpe/module.py|read|159])