mailman: monitor listinfo page (of wikimedia-l)

RT #7878

PS4: make it actually check for content strings

PS5: split patch to just contain the check for listinfo page,
     this doesn't work yet for the archive links because they
     redirect from http to https, not the other way around

Change-Id: Ifd3904984bf3417f0dd8fde343d679160b637676
Merge "mailman: monitor listinfo page (of wikimedia-l)" into production