Make stackviz tasks not to fail jobs

Due to issue on stckviz side, job start
failing with POST_FAILURE. If we fix the
issue still we need to wait for periodic job
periodic-package-stackviz-element to publish
the latest tarball on https://tarballs.openstack.org/stackviz/dist/.

Let's not fail the job for any issue occur during
stackviz processing.

Closes-Bug: 1863161

Change-Id: Ifee04f28ecee52e74803f1623aba5cfe5ee5ec90
(cherry picked from commit 580fec54)