Otherwise yum priorities plugin will ignore them

The default `prepareImage.sh` will create an image with cern-only repositories inside. Run `prepareImage.sh public` to use another dockerfile, that forces package installation from public sources.

This new build method allows to remove the *complex* `rename:dockerimage` stage.

[cta-taped] The MaintenanceProcess can be disabled via its configuration file (DisableMaintenanceProcess)

[repack] Corrected the problem of Agent ownership removal for repack request and repack sub-requests

Adding some checks on available rpms to fail Docker build phase if there is no point going further (with some diagnostics)

Updated cta-taped.conf.example to show how to disable the Repack Request Management on the tapeserver

[cta-taped] The repack management can be enabled or disabled via the DisableRepackManagement parameter in the configuration file

[RAO] If the drive limits UDS could not be queried, the RAO is not disabled anymore. A CTA RAO is triggered.

This reverts commit 2973d275.

And improve starting of old and new versions of mhvlt when creating buildtree environment

By default all packages will be taken from public repositories. Run `./bootstrapCTA.sh cern` and `./bootstrapMHVTL.sh cern` to get packages from cern-only repos.

This reverts commit 18b07b1f.