Remove tiered building in build.py

Many tiers have been shed over this issue and frankly enough is enough
on this tiering thing, it's tiering us apart! Now we use threading a
bit better as well.
No more tiers! Puns very much intended.

Additionally, this refactors the function names to make inc0 happier
and be consistent.

We also modify the test_build.py to catch the new statuses introduced
by the regex patch. Then we remove the Ubuntu Source from the Docker
folder test as that will never ever be functional.

Also fixed regex to properly match true regex expressions.

Co-Authored-By: Michal Jastrzebski (inc0) <michal.jastrzebski@intel.com>
Change-Id: I650fd6af76eddb809756762222e66aefd6fc1dca
Partially-Implements: blueprint build-script