Preparations for the Bigtop 0.6.0

[Roman Shaposhnik]

Hi!

I've scrubbed most of the obvious items in our JIRA (sorry
for the spam) but we still have 49 issues left assigned to
Bigtop 0.6.0:
    https://issues.apache.org/jira/browse/BIGTOP/fixforversion/12323895

I would appreciate all your help in either fixing those or
triaging and pushing them out into Bigtop 0.7.0.

If you're not sure what to do -- holler on the ML!

Thanks,
Roman.