Disable coverage for now

This is to make tests run. Currently we are not using coverage reports,
and a recent fix to remove development dependencies from the normal
installation has caused coverage dependencies to be removed and thus
fail.

We will revert this once we figure out how to make tests run with
separate bundler groups.
Reference github issues now.

Hosted Jira (logstash.jira.com) is currently busted because we have
exceeded the maximum number of users that platform can accomodate
(according to Atlassian support). Until that is resolved, let's point
everyone at github issues instead.

closes #1508