qa/common.filter: add per-distro babble filter hook for service startup
qa/common.filter: add per-distro babble filter hook for service startup

Service startup generates incomprehensible babble on some platforms.

Example is a line containing just "S" from pmcd startup on Debian
unstable ... don't even ask how this happens.

As per Mr. Plod's direction "Just move along, nothing to see here",
so filter this nonsense away.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp