We recently removed nenutron.common.rpc [1] as the rpc module lives in
neutron-lib now. This project was missed because I didn't find
neutron.common.rpc as an import. This patch switches rpc uses over to
neutron-lib.
This also addresses an issue where toxenv fails when it encounters a
non-empty __pycache__ directory. This adjusts the options passed to
find so that it is tolerant of this scenario and allows tox runs to
proceed.
[1] https://review.openstack.org/#/c/634790/
Change-Id: Ice83f7574f146436e3db045693b530f0cfeda049
19aed83ff1