Add Java e2e tests

[jasonjkeller]

Resolves newrelic/newrelic-java-agent#1860
Resolves newrelic/newrelic-java-agent#1861

[tippmar-nr]

Actually, the problem is that the "Build init container for e2e test" step isn't setting an agent version:

#4 [2/3] ADD https://download.newrelic.com/newrelic/java-agent/newrelic-agent//newrelic-agent-.jar /newrelic-agent.jar
#4 ERROR: invalid response status 404

@jasonjkeller Is there an "unversioned" latest release of the Java agent that you can reference here? We had to do a little bit of dancing on the .NET side to add an unversioned tarball to our release process to accommodate this particular use case. There really won't be a way for the tests to be supplied with a version number - so I think Java will either need an unversioned jar file or some other way to get "latest version".

Edit: Looks like you could reference https://download.newrelic.com/newrelic/java-agent/newrelic-agent/current/newrelic-agent.jar and be in good shape!

[jasonjkeller]

@tippmar-nr Thanks. I ended up moving the agent download logic into a little shell script invoked by the init container Dockerfile that will download the agent version matching the build arg if it's provided, otherwise it will just default to the current version. That seems to have done the trick.