Pin detox
Pin detox

detox 0.19 is not compatible with the version of tox we are
getting from upstream

Signed-off-by: Anil Belur <8d20583206dd5998eef71c68978f72fb46efdafa@linuxfoundation.org>
Change-Id: I1e4284709702d99125927d945af4c4ee90f0dd96

opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt