- on Ubuntu Xenial, `python-virtualenv` package no longer installs
`virtualenv` shell script.
Change all `virtualenv` invocations to 'python -m virtualenv',
which is more portable.
- in `pip_install.yml`, add `virtualenv_command` argument using
the same portable invocation.
- in `install-deps.sh`, the condition to install `python-virtualenv`
was missing the `not` part
- the venv is created with `sudo` elevation in `install-deps.sh`,
thus in `env-setup.sh` Ansible must be installed into venv
using `sudo` elevation as well.
- in `install.yml`, fix passing `bifrost_venv_dir` var to `pip_install.yml`
Change-Id: Ifaa54a0dc97ed59ca8360e62878b603a04105e46