Restore parsing of configuration file

For some reason, parsing of configuration files seem to have been removed in https://github.com/brianlmoon/GearmanManager/commit/70718c71a16f085b7aa320123a15c9f3eb2dd400#diff-4ef92d5970f5612c2d2d8ea8c16a7df9. This should return that functionality by re-adding the parse_config function call.