twmeproxy: monitor the memcache port as well

We just had a complicated failure scenario where the root cause was that
twemproxy had stopped listening on the 11211 port but kept running and
listening on the 22222 management socket. twemproxy didn't log anything
anywhere and strace/gdb didn't reveal more, so this remains a puzzle for
now.

In the meantime, add an NRPE check to monitor 11211 as well so that at
least we can be alerted if/when that happens again.

Change-Id: I09c0fce64160e6d58f2a85599dd17c57e4aa923d
Merge "twmeproxy: monitor the memcache port as well" into production