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We do not need tox_install.sh, pip can handle constraints itself and install the project correctly. Thus update tox.ini and remove the now obsolete tools/tox_install.sh file. This follows https://review.openstack.org/#/c/508061 to remove tools/tox_install.sh. Change-Id: Ie7c06ead39c8597ec9326f223625d1fa0d5208d1