ensure we run db tests in CI

CI had a set of environmental variables that refused to allow the
tests from failing gracefully. These seem to have gotten lost
along the way in refactoring.

Change-Id: Ib19b5d472c51ed72b8acf1571dd19f41474532c5
libvirt: fix volume walk of /dev/disk/by-path

If /dev/disk/by-path does not exist, then _get_iscsi_devices() will
raise an IndexError. Handle this case and return an empty list. This
fixes a test on OSX.

Fixes bug 1130841

Change-Id: Ibae2f1238feac9a10b8dc2b74886ea59edac0bcc
Merge "libvirt: fix volume walk of /dev/disk/by-path"
Merge "ensure we run db tests in CI"