Add -U to pip install command in tox.ini
Add -U to pip install command in tox.ini

Ask pip to upgrade packages in the virtualenv so that a long-lived
virtualenv is still kept up to date as external dependencies change.

Change-Id: Id1e83aa5dd7c39d4827baeb39827b0ddeb8b6d4a

metacloud/python-troveclient,openstack/python-troveclient,metacloud/python-troveclient,openstack/python-troveclient,Tesora/tesora-python-troveclient,Tesora/tesora-python-troveclient