Change Pedant config default location

The existing default was for OPC, and doesn't make much sense anymore.  This makes the default a "pedant_config.rb" file in the current directory.

We could just make the config file a mandatory argument, but that would require further changes in our omnibus-ctl "test" task definitions (which is not necessarily an argument against that option; just pointing out what it would entail)

cc @hosh @seth @schisamo