Isolate tests running as root locally

[nirs]

Some tests like storage tests (lvm, blocksd) require root. It is possible to run them
like this:

sudo ~/.venv/vdsm/bin/tox -e storage tests/storage/lvm_test.py

But after that, some files in .tox, tests and /var/tmp/vdsm are owned by root, so
the next tests run as regular user will break with permissions errors.

Developers can fix this using:

sudo chown -R $USER:$USER .tox tests/htmlcov* /var/tmp/vdsm

But this is ugly. We need an easy way to run tests as root that does not require any
cleanup after running the tests.

One way to fix this is to use separate directories for:

• Pytest temporary directory (pytest has solution for this)
• .tox directory
• tests/htmlcov* directories

Another way is to run the tests in a container, but some lvm tests do not work in a container.

[aesteve-rh]

I think this issue may be already covered in #276 .