Add Java 11 to Pulsar Build image and upgrade dependencies

[eolivelli]

• add Java 11
• remove Java 8
• set Default Maven version to 3.6.3
• add Python3/Pip3
• upgrade Go to 1.13

I had to upgrade Go to 1.13, otherwise the build of the image would fail with this error
golang/go#34202

I had to set the MAVEN_VERSION ARG in order to allow the build to pass

[eolivelli]

@merlimat @aahmed-se @lhotari PTAL

After committing this patch we should deploy the build image.
The default regarding Maven is not changed.

The only notable changes are:

• now we have python3 (instead of python2)
• now we have Go 1.13 (instead of 1.10)

[aahmed-se]

I would change things start with neewer base image that only has jdk 11 and python3 as default.

[eolivelli]

I believe that the transition won't be easy.
We should deploy the new image and start running tests on jdk11 but I guess it will take time to stabilise them.
In the meantime the default jdk is 8 and current CI jobs should continue to run without changes.

[aahmed-se]

Don't see the point of the modifying the current image. We can start with a new image base run the jobs with allowance for failure in parallel.

[eolivelli]

@aahmed-se I have dropped JDK8.

I am not sure about the removal of Python 2.7. I guess it will complicate the transition to JDK11.

My point here is to allow CI to run on JDK11, if we make too many changes than the work will be bigger and bigger

[aahmed-se]

@eolivelli this is fine enough changes for one pr, lets try to get the tests to pass.

[eolivelli]

/pulsarbot run-failure-tests

[sijie]

@merlimat @eolivelli and I discussed this in the community meeting. I think we want to keep JDK8 around for backward compatibility consideration. i.e. build a Java8 compatible release using JDK11 and validate it can run with JDK8.

[eolivelli]

@sijie @merlimat @aahmed-se I have restored the support for JDK8 PTAL

[eolivelli]

@aahmed-se please review again

[eolivelli]

/pulsarbot run-failure-tests

[eolivelli]

please note that the CI is not using this image (so basically CI tests are useless apart from RAT/license headers tests)

[eolivelli]

@aahmed-se @merlimat CI passed, can you please merge this patch and publish the new docker image ?