nagios: introduce a new check_sslxNN check

We currently have 101 cache servers and 12 second-level domains. Since
we recently moved SSL termination into the cache servers and we started
using SNI with a separate certificate per domain, we have increased our
check_ssl checks to 2626.

Besides creating quite the bit of load for the Icinga server, this is
also noisy: if an SSL server is misconfigured, we'll get dozens of
alerts. Even worse, since all of these certificates were bought close
together, at the time of their expiry we'll get thousands of alerts.

Introduce a new check_sslxNN check that calls check_ssl internally NN
times, where NN currently is ('', 'en.', 'en.m.') x (domains) i.e.
3x12=36. This is made in an special, hacky way that allows us to avoid
the whole fork/exec dance but perform this optimally with Perl and
minimum overhead.

This means that we'll still get a hundred alerts on certificate expiry
time but solving this is going to prove more difficult.

Change-Id: I654151b97ea246d290265a03fb80a108344781b0