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: I22c434f6c96c369a8357f6bfd3208a1270c2c849

stackforge/python-senlinclient,openstack/python-senlinclient,openstack/python-senlinclient,stackforge/python-senlinclient