component isolation: introduce models and database schema

The so called component isolation feature needs to keep track of
more information than we usually do with the AFE/TKO models.

I've decided to loose the afe_ and tko_ suffixes on the database
tables because there's a trend towards uniting the database. Also,
the component isolation deals with some aspects and models on both
AFE and TKO, so it doesn't make sense to pick a side.

If you have a running database, those changes should be applied with:

   $ cd AUTOTEST_ROOT/frontend
   $ ./manage.py migrate afe
   $ ./manage.py migrate tko

If you're creating a database from scratch, no extra step is needed.

This also preloads the database with "unknown" entries.

The unknown distro will be used either when the test does not
register or is able to detect the linux distro it's running on.

The unknown software kind and arch are also used as fallbacks
when not properly recorded.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
autotest-distro-def-load: add utility scripts

This scripts allows a user to load a distro definition file into
the autotest server database.

Signed-off-by: Cleber Rosa <crosa@redhat.com>