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.
tox_install.sh was also building ovs for functional test. Move this into
tools/setup-ovs.sh and call it from functional tox environment.
Change-Id: I5857c8ae3e945328c0f24bda37629ce7e0faefa7
163ee83ce8