Update priorityClassName default values in READMEs

[tanordheim]

Updates READMEs for the elasticsearch, filebeat and kibana charts to clarify that the default value of priorityClassName is an empty string, re a discussion in #248.

I've made the change in one commit per chart, let me know if you'd rather want these squashed into a single commit.

• Chart version not bumped (the versions are all bumped and released at the same time)
• README.md updated with any new values or changes
• Updated template tests in ${CHART}/tests/*.py
• Updated integration tests in ${CHART}/examples/*/test/goss.yaml

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[Crazybus]

LGTM!

I've made the change in one commit per chart, let me know if you'd rather want these squashed into a single commit.

Nope this looks great!

Thank you for so quickly following up...it was almost too fast so I think you might be a robot ;)

[tanordheim]

Thank you for so quickly following up...it was almost too fast so I think you might be a robot ;)