Python venvs are not particularly portable. To overcome this
problem we have a bunch of stuff implemented to fix them
after we unpack them. This ranges from relatively simple
things like re-implementing python in the venv and changing
the shebangs for everything in it, to more complex things
like having to package a venv per distro/architecture.
All of this can be eliminated by simplifying the mechanism
into just creating the venv on the target host, and installing
the python packages into it. To help speed up the build, we
can simply build wheels before hand and store them on a web
server somewhere.
This patch implements the changes to:
1. Do away with packaging the venv.
2. Keep it simple. We install into the venv, and that's that.
3. Add a toggle to rebuild the venv if you'd like to.
4. Use import_tasks with tags for each stage so that it's
easy to skip a portion of what executes.
Change-Id: I708b5cf32e5cce6a18624d0b3be0cd4c828ad389
ac5e5e9283