Changes

jobs/coverity: fix clean up permission errors

Don't mount the host's osmo-ci/coverity dir in /build/osmo-ci/coverity.
The current working dir is mounted as /build, and because docker creates
the /build/osmo-ci directory structure as root, we end up with having
subdirectories created by root in our current working dir. These then
cause an error on the next run when jenkins tries to clean them up.

Fixes: 6a2451a0 ("jobs/coverity: adjust mount path to new home dir")
Change-Id: Ie0aa02d3821df6d0505748a7dd70ff67e4cf1405