[Linaro-validation] Skipping 2015.11 availability on Trusty

[Neil Williams]

It has become impractical to maintain support for the latest production
releases on Ubuntu Trusty 14.04LTS due to behaviour required by the
server side changes needed by the dispatcher refactoring. These are
important changes and are impractical to backport to the version of
python-django available in Trusty.

I have tried working around the issues but it involves pulling more
dependencies from Jessie or Vivid and in my tests, the existing
installation became confused and failed to install due to problems with
the database migrations. The LAVA software team do not have the
resources to maintain backports of the complete dependency chain in
Ubuntu, it is a much more manageable set in Debian Jessie (where the
same migration went without issues on multiple machines).

The changes in 2015.11 are almost exclusively related to the dispatcher
refactoring and therefore there is expected to be limited impact on
current installations on Trusty.

For the next release, we will investigate code changes which omit the
new support for Trusty builds but this will have the effect of
preventing those installs from working with the pipeline and the new
YAML job submissions. The documentation for Trusty will also be
updated, if necessary as a hotfix to 2015.9 just for Trusty.

If the code changes do not work cleanly, then the current 2015.9 (and
the documentation hotfix to follow) would become the last LAVA releases
for Ubuntu Trusty 14.04LTS.

Users of Ubuntu Trusty 14.04LTS are reminded that a new LTS is due for
release in April 2016 but that the LAVA software team are not using
Trusty any longer. Any issues with the migration from Trusty to the
new LTS are outside of our control.

Migrating an instance from Ubuntu to Debian would involve dumping and
re-importing the database - bear in mind that Trusty has postgres9.3 and
Jessie has 9.4, so care will be needed to migrate the postgresql
cluster correctly - there is documentation for that migration in the
lava-server docs. It is not recommended to attempt to migrate the OS
itself from Ubuntu to Debian (or vice-versa), a reinstall is a better
option, so make a backup and ensure that the backup works.