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: I3a6c85db180c25e360934ada60df7328ed7a765a