Bump subscribe throttle to 10 seconds

Waiting for only 9 seconds is not enough, for instance see
https://travis-ci.org/Fullscreen/yt/jobs/25291112 -- the test fail
because we only wait for 9 seconds between subscribing to a channel
and checking if that subscription exists.

Hopefully 10 seconds will do.
Merge branch 'bump-subscribe-throttle'