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: I203405c7eee1c5abbc9ec19901493674f40879ee

openstack/glance,openstack/glance,klmitch/glance,rajalokan/glance,dims/glance,openstack/glance,rajalokan/glance,stevelle/glance,dims/glance,klmitch/glance,stevelle/glance