Added reload to the NRPE client service & modified the LWRP to call reload

Added reload to the NRPE client service & modified the LWRP to call this rather than restart. This stops unneeded crits being generated as a result of adding or removing a check via the LWRP - reloading NRPE is graceful, restarting is not.

(initially opened as https://github.com/tas50/nagios/pull/265 before realising this had been split out.)