MINOR: haproxy: Add `-cc` argument

MINOR: haproxy: Add `-cc` argument

This patch adds the `-cc` (check condition) argument to evaluate conditions on
startup and return the result as the exit code.

As an example this can be used to easily check HAProxy's version in scripts:

    haproxy -cc 'version_atleast(2.4)'

This resolves GitHub issue #1246.

Co-authored-by: Tim Duesterhus <tim@bastelstu.be>