`!buildbot` PR command matches each word

[encukou]

I didn't investigate very deeply, but it seems that:
Since the 4.0 upgrade, the !buildbot command starts more buildbots than before, while @bedevere-bot's comment lists only ones that would be matched before.

Presumably the comment code and scheduler are now out of sync.

[vstinner]

Since the 4.0 upgrade, the !buildbot command starts more buildbots than before

I saw this issue before, I'm not sure that it's a regression caused by the buildbot 4.0 upgrade.

[pablogsal]

I think this is a consecuence of #419