Improve alerting so that largest cluster wins, not the one with the best fit.

BUG=skia:

Review URL: https://codereview.chromium.org/661723003
Cleanup from the first CL to setup Grafana/InfluxDB.

Adds more detail to README.md and also renames some config files to more
explicit names.

BUG=skia:

Review URL: https://codereview.chromium.org/649543005
logserver: Fix typo in port flag.

It was changed from 8001 to 10115 by commit in
https://skia.googlesource.com/buildbot/+/4bac1fffb3bd4015fec5f0517c9c084b14085adb

BUG=None
TEST=None
R=jcgregorio@google.com

Review URL: https://codereview.chromium.org/652663007
Move prober to built like all other Go apps.

BUG=skia:

Review URL: https://codereview.chromium.org/643903004