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: I54c35e61d889852dfcff34acc841da7efa556f1d

hayderimran7/ec2-api,openstack/ec2-api,openstack/ec2-api,hayderimran7/ec2-api,stackforge/ec2-api,stackforge/ec2-api