Nova providers did not previously have region support, so things like
the host aggregate provider do not work as expected in a multi-region
environment. This change mirrors what puppet-neutron's providers do,
they use the nova_region_name setting, this uses neutron/region_name.
Change-Id: I1d5bddbe977352b0458115ab77b8129311b63453
Closes-Bug: #1517220
b58a02139d