The steps involved in the various repository tool scan_for_server

implementations were overcomplicated and ugly. The main command would

check the option (which includes the config value), and then failing

that, delegate to the repository tool. The repository tools would then

check the config value again before scanning any repository-specific

storage locations like SVN attributes or P4 counters. This second config

step also looked in the TREES config key, which was something from

extremely early on in RBTools' life and has never been properly

documented or expanded upon in the intended ways.
This change cleans up the individual tool scan_for_server

implementations to only perform checking repository-specific methods.

The check for the TREES config has been moved to the very end of the

process as a fallback, and will emit a warning that such a configuration

is deprecated and will be removed.

Ran unit tests.
Set up a configuration that used the old TREES method and saw the

  expected warning.