Use a local settings file for rt-test server.js, add more options.

The round-trip test server will now read a server.settings.js file for its
options, including MySQL connection settings. The command line options
can still be used and they will override those present in the file.

There are also 3 new configuration parameters:
- 'tries' establishes the number of times a title is tested for a commit hash
before it's considered an error.
- 'fetches' sets the number of fetching errors that will be accepted before
the title is no longer considered for testing.
- 'cutofftime' represents, in seconds, the time to wait for a valid response
from a client.

Bug: 52114
Change-Id: If877269980931157ee2e94996edfa4e473a6f610