Fail maven builds when gulp tasks throw errors

To make sure that we can both guarantee that gulp tasks throw an exit code 1 after an error (eslint didnt) and at the same time are able to develop using gulp.watch we have added a --fail-on-gulp-error flag to the hippo-build.

In your maven project the gulp-build execution should be formulated as follows:

<execution>
  <id>gulp-build</id>
  <phase>process-resources</phase>
  <goals><goal>exec</goal></goals>
  <configuration>
    <executable>npm</executable>
    <commandlineArgs>run gulp buildDist -- --fail-on-gulp-error</commandlineArgs>
  </configuration>
</execution>

And your gulp-test execution should be formulated as follows:

<execution>
  <id>gulp-test</id>
  <phase>test</phase>
  <goals><goal>exec</goal></goals>
  <configuration>
    <executable>npm</executable>
    <commandlineArgs>run gulp test -- --fail-on-gulp-error</commandlineArgs>
  </configuration>
</execution>