make validators errors clearer

[galcohen92]

in case of ajv error it return it under the schema endpoint, instead should return array of errors in case of validaiton fail. in case of success validation return empty array.

example:

 let validationErrors = schemaEndpoint.parameters.validate({ query: {},
                headers: { 'host': 'test' },
                path: {},
                files: undefined });
            expect(validationErrors).to.be.eql([
                {
                    'dataPath': '.headers',
                    'keyword': 'required',
                    'message': "should have required property 'api-version'",
                    'params': {
                        'missingProperty': 'api-version'
                    },
                    'schemaPath': '#/properties/headers/required'
                }
            ]);