Add script to filter jenkins notifications

it works as a webhook receiver CGI
and produces email output about interesting results
Add travis syntax checking
reindent all bash scripts to make them bash8 compliant

also add a test for it
slight reworking of mkcloud-crowbar-logs.sh
Remove adding of local repos to the admin node in TESTHEAD setups

Clarify documentation that TESTHEAD picks up the media from
Staging and tests it against the update-testing repositories.

The extra repos like Devel_Cloud_Shared and the like were only
breaking the run most of the time, and we should really test the
media only - otherwise packages might be available that have
been forgotten from the media.