Fixes #17330 - skip admin email if it's unknown

When admin user is being seeded the Setting might not exist at that
moment. We can't just create it with value, since the setting would
be invalid because of other attributes. Therefore we split settings
creation from the setting list so we could create it from seed too....

Fixes #17837 - Fix hosts:scan_out_of_sync task

The task relies on Ping, which was removed since Ruby 1.9. I've moved it
to rely on net-ping instead. Notice the ping now relies on the 'ping'
binary being in the foreman user path for this to work with foreman-rake

Fixes #1556, #11615 - Remove puppet rdoc support

Puppet rdoc support has been broken for a long time. Removing it from
Foreman.

Fixes #17488 - Add confirmation to import db task

fixes #17474 - DROP db prior to restore on postgres

when using postgres as a database, and restoring and
existing db dump, clean the target database prior to restore.

this allow the usage case when installing a new server,
running foreman-installer and then restoring the database.

Fixes #17361 - ensure plugins migration paths are set

fixes #16557 - move tests into modern Rails layout

Models, controllers, mailers and helpers are now in test/ subdirs
matching app/ subdirs. Service, miscellaneous and old test/lib/ tests
are now in test/unit/ separated from models, which obsoletes the custom...

Fixes #16565 - Correct host search by parameters

Overrides for parameters values caused incorrect results for when
searching by parameter value. This commit fixes those results, and
improves the handling of parameter priorities in general. A new rake
task, `parameters:reset_priorities` is introduced that should be invoked...

fixes #16529 - require rake/testtask explicitly

Fixes #12634 - New HW Model flag pxe_loader

Implementation of

https://github.com/theforeman/rfcs/blob/master/text/0001-PXE-Booting-UEFI.md

In short, new host/hostgroup flag PXE loader is added to specify TFTP
DHCP filename and Foreman now orchestrates all PXE-capable templates...