CI fix and improvement

All CI problems fixed + some improvements. Now the CI features 3 stages:

1. build: install a Python virtualenv in current CI job directory, install correct pip version in the venv (the one installed on the CI machine is outdated + force a specific version compatible with current setup.py of power-modeling package), install power-modeling in the venv
2. test: perform a quick alive test with power-modeling in the venv
3. deploy: if everything works, deploy power-modeling in the persistent virtualenv on the CI machine (in the user directory) for the other tools and use cases to use it