Speedup assigning non-blocking categories (`mtype`)

[iarspider]

Function add_nonblocking_labels:

• Use set for extra_labels["mtype"]
• Once a label is assigned from one file, no need to change other files

[cmsbuild]

cms-bot internal usage

[cmsbuild]

A new Issue was created by @iarspider.

@Dr15Jones, @antoniovilela, @makortel, @mandrenguyen, @rappoccio, @sextonkennedy, @smuzaffar can you please review it and eventually sign/assign? Thanks.

cms-bot commands are listed here

[iarspider]

See if getting watchers can be sped up:

watchers = set(
            [
                user
                for chg_file in chg_files
                for user, watched_regexp in list(WATCHERS.items())
                for regexp in watched_regexp
                if re.match("^" + regexp + ".*", chg_file) and user != author
            ]
        )