In certain environments the load order can be confused between nova
and zun. This can cause boot issues where 'No module named cmd.compute'
can be thrown because the python code is looking in zun/nova for that
driver.
This change extends the declare_namespace code to allow for the other
projects to properly load.
Similar fix: https://review.openstack.org/#/c/311724/
Closes-Bug: #1650107
Change-Id: Ibb12f73a378dcc30a0483422226f57d52b53fde9
2909374a77