runner: Exit 8 if every test was skipped or otherwise ignored
Closes: #901804
Probably shouldn't be merged until https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=901846 is implemented in debci and https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=901847 in britney.
Edited by Simon McVittie