Increase the max file size for the flakiness dashboard to 30mb.

We have a couple bot that are hitting the current 20mb limit. That's
kind of absurd, but there's work in progress to make the json more
compact. In the meantime, this avoids 500s and keeps everything functioning.

Also, increase the min time for pruning for debug bots so we prune
more and make the JSON smaller. We increased the default timeout for
debug bots, so it makes sense to increase this as well.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/19968006

git-svn-id: svn://svn.chromium.org/blink/trunk@154685 bbb929c8-8fbe-4397-9dbb-9b2b20218538