Raise ExternalTimeout for htmltest (#4158)
Raise ExternalTimeout for htmltest (#4158)

Got a failure for https://graphite.readthedocs.io/en/latest/functions.html -- the site might just be slow. Spurious failures here seem likely,
so bumping timeout to 30s.

commit-id:ca6d5bdc
m3db/m3db,m3db/m3db,m3db/m3db,m3db/m3db