Use upper-contraints in the gate jobs

[Devdatta Kulkarni]

Currently Solum gates don't seem to use upper-contraints on requirements. This might lead to issues like what Barbican ran into recently with new release of Pecan [1].

One solution to that is to use upper-contraints in our gate jobs as done in [2].

Currently, solum [3], python-solumclient [4], or solum-dashboard [5] none seem to be using upper-contraints.

We need to submit patches similar to [2] to add upper-constraints to solum repositories.

[1] http://lists.openstack.org/pipermail/openstack-dev/2016-September/104562.html

[2] https://review.openstack.org/#/c/358404/1

[3] https://github.com/openstack/solum/blob/master/tox.ini

[4] https://github.com/openstack/python-solumclient/blob/master/tox.ini

[5] https://github.com/openstack/solum-dashboard/blob/master/tox.ini