Remove --verbose and --debug CLI flags

These aren't used. Remove them prior to refactoring.
Replace methadone with optparse and tests

This is essentially the same as alphagov/vcloud-edge_gateway#70. The
executable has been rewritten to use plain OptionParser and unit tested.

With the difference that exceptions are caught to prevent the stacktrace
being leaked to the CLI to preserve existing behaviour.
Merge pull request #78 from alphagov/72169082-test_executable

[#72169082] Replace methadone with optparse and tests