Add the check_memcached.pl Icinga plugin

Add the check_memcached.pl Icinga plugin

This adds the check_memcached.pl script to the /usr/lib/nagios/plugins directory
on all monitor servers and defines a custom command on monitor servers to check
the performance of the memcached program.

Default warn/critical metrics for response_time were also increased based on trends
seen in PINES production via visualization with pnp4nagios graphing over the past
7 months.

Signed-off-by: Michael Peters <mpeters@emeralddata.net>
Signed-off-by: root <root@pines-dev-ubuntu.gapines.org>
Signed-off-by: Michael Peters <mpeters@emeralddata.net>