Update known issues for Gerrit v3.1[2-4]

The known issues of Gerrit v3.12, v3.13 and v3.14
release notes were incomplete or stale. If an issue is resolved
can be removed from the known issue; however, if the issue still
persists across releases, it must be carefully ported across
releases.

Having the known issue mentioned in the release notes
is highly beneficial for all of those who are upgrading
skipping intermediate releases.

By making the small adjustments indicated in the known issues
section of the release notes, Gerrit admins can prevent problematic
outages or malfunctioning between upgrades.

Change-Id: I79da6179657af44546b468ee8ba3520b8f2e3cc8