[BEAM-2080]: Add a custom enforcer rule to check for banned classes.

[vikkyrk]

Be sure to do all of the following to help us incorporate your contribution
quickly and easily:

• Make sure the PR title is formatted like:
  [BEAM-<Jira issue #>] Description of pull request
• Make sure tests pass via mvn clean verify. (Even better, enable
  Travis-CI on your fork and ensure the whole test matrix passes).
• Replace <Jira issue #> in the title with the actual Jira issue
  number, if there is one.
• If this contribution is large, please file an Apache
  Individual Contributor License Agreement.

---

• Add a custom rule to catch banned classes which can be specified using full path like org/apache/beam/Foo.class or using wildcards like org/apache/maven/**
• Disable enforcer plugin in parent pom to avoid circular dependency issues with the custom rule
• Move enforcer executions to pluginManagement and explicitly include them in sdks, examples and runners.

[vikkyrk]

R: @davorbonaci . Feel free to add other maven experts in the team for review if needed.

[jbonofre]

Thanks for the contribution ! Can you provide a quick abstract about the enforcer rule ?

[vikkyrk]

@jbonofre The enforcer rule that I have added in this PR basically looks at all the classes within the artifacts generated by Beam (like sdks-core-*.jar, examples-*.jar etc.) and makes sure that we do not included unintended classes like com.google.guava or org.apache.maven etc. (configurable from the pom file). This is particularly useful for when using shade plugin to build a uber bundled jar but accidentally forget to shade libraries like guava.

[vikkyrk]

Retest this please

[vikkyrk]

Retest this please

[coveralls]

Coverage increased (+0.007%) to 70.2% when pulling 827c6e4 on vikkyrk:mvn_enforcer into 13c06bf on apache:master.

[kennknowles]

Since development here, we've started migrating to Gradle. This same functionality might be handy in a Gradle task of some sort. Are you planning on working on this any more?

[stale]

This pull request has been marked as stale due to 60 days of inactivity. It will be closed in 1 week if no further activity occurs. If you think that’s incorrect or this pull request requires a review, please simply write any comment. If closed, you can revive the PR at any time and @mention a reviewer or discuss it on the dev@beam.apache.org list. Thank you for your contributions.