Install os-refresh-config from release into a venv

We had been installing this from a git repository into the global site-packages.
Which is inconsistent with how we install os-apply-config.

Change-Id: I1a2167d3e71cc97bd387191b44eb4d59b62ce00c
Don't install python-pip

We're using pip from the virtual environment.

Change-Id: Ica5d918501018c4acd7e46b6b1265f8ec4ffe8a1
Don't install git-core

This was used required back when the pip install referenced a
git+https://... url and is no longer required.

Change-Id: Id4243712ece3c847ad26d585448bff20b2aae8fe
Merge "Install os-refresh-config from release into a venv"
Merge "Don't install python-pip"
Merge "Don't install git-core"