Use a common python build/install role
In order to radically simplify how we prepare the service
venvs, we use a common role to do the wheel builds and the
venv preparation. This makes the process far simpler to
understand, because the role does its own building and
installing. It also reduces the code maintenance burden,
because instead of duplicating the build processes in the
repo_build role and the service role - we only have it all
done in a single place.
We also change the role venv tag var to use the integrated
build's common venv tag so that we can remove the role's
venv tag in group_vars in the integrated build. This reduces
memory consumption and also reduces the duplication.
This is by no means the final stop in the simplification
process, but it is a step forward. The will be work to follow
1. Replaces 'developer mode' with an equivalent mechanism
that uses the common role and is simpler to understand.
We will also simplify the provisioning of pip install
arguments when doing this.
Implements: blueprint python-build-install-simplification
Signed-off-by: Jesse Pretorius <firstname.lastname@example.org>