Supports selecting a match when more than one pattern may match for
regex and prefix matching.

The problem in Varnish issue #2880 comes about when len >= 49.

Closes #19

Thanks to @martin, @slink and @lf for their comments.

For sharding: we get the http port number from the Endpoints of the
Varnish service. From the PodSpec and -Status we get the host
name and the PodIP.

Initially to publish workqueue metrics.

Workaround for Varnish issue #2880:
https://github.com/varnishcache/varnish-cache/issues/2880

Refactor the test sources a bit while we're here.

Also shorten some names that predictably include '.' -- Service
backends and Host strings.

'compare' can be one of equal, not-equal, match or non-match.

'value' is either a fixed string for (in)equality tests, or a
regex to test for (non-)match.

This makes it possible to set values for the invocation via env
variables in the pod template, in particular to use PROXY.