Deprecated tox -downloadcache option removed
Deprecated tox -downloadcache option removed

Caching is enabled by default from pip version 6.0

More info:
https://testrun.org/tox/latest/config.html#confval-downloadcache=path
https://pip.pypa.io/en/stable/reference/pip_install/#caching

Change-Id: I41223342a691defad200dbfdc45c6df6bc37c314

stackforge/group-based-policy-ui,noironetworks/group-based-policy-ui,noironetworks/group-based-policy-ui,noironetworks/group-based-policy-ui,stackforge/group-based-policy-ui,stackforge/group-based-policy-ui,noironetworks/group-based-policy-ui,stackforge/group-based-policy-ui