Misc fixes to bring tox targets back inline with general OpenStack
standards (py27 and py35 targets executed by default).
Deal with running 27 and 35 tests in succession.
This change also includes some fixes for coverage reporting; however
they are still currently broken due to mismatching module names
between nova-lxd and nova.virt.lxd.
Change-Id: If0079309a4c4b6b57fc6b5e6f0e947926b010f09
James Page