Remove git and jq dependency in most scripts, allowing to run them on
latest atomic images, or even distribute Kolla in the form of tarball.

The only remainings of git dependency are in the git pre-commit hook,
and in the image build scripts. We can remove the latter one and have
the scripts running in degraded mode if we really want to.

I opted for a python based approach to finding the top-level directory
for portability, ensuring consistent result on Linux and BSD, including
OSX.

Change-Id: I987174032d11b2e9d6a993c563b5dc877c15dd2d