1. Variables have been renamed to make it easier to
understand their purpose.
2. Unnecessary variables have been removed.
3. The role no longer caters to installing pip packages
on the host. This should never be necessary - if it
is, then something should do so beforehand.
4. The expected versions of pip/virtualenv are documented
and a check has been added to ensure that they exist.
5. The handler has been named to make debug logs less
confusing.
6. The default storage path for venvs/wheels is no longer
opinionated. If paths based on distro/architecture are
required then different paths should be provided to
the role.
Change-Id: I9eb96e9db22f918b00456af943d81f66050107ce
d169906c68