docs: function _validateInput(schema, config, cb) {
      var ajv = new Ajv({allErrors: true, verbose: true, format: 'full'});
      var validate = ajv.compile(schema);
      var valid = validate(config);
  
      if (!valid) {
          // ajv does not return a real error object, hence the dance here to
          // produce real errors.
          var errors = _.map(validate.errors, function (fakeErr) {
              return new verror.VError({
                  name: 'EnrouteConfigValidationError',
                  info: fakeErr
              }, 'config validation error');
          });
          var err = new verror.MultiError(errors, 'Invalid input');
          return cb(err);
      } else {
          return cb(null, _.cloneDeep(config));
      }
  }