install-deps.sh: pip wheel for python dependencies

install-deps.sh: pip wheel for python dependencies

For all tox.ini in the source tree which also have requirement.txt
files, create a wheelhouse with the dependencies. This allows tox to
setup test environment with no access to the network with something
like (in tox.ini):

        deps =
          --use-wheel
          --find-links={toxinidir}/wheelhouse
          -r{toxinidir}/requirements.txt
          -r{toxinidir}/test-requirements.txt

Signed-off-by: Loic Dachary <ldachary@redhat.com>