Use udev-created device as default Azure ephemeral disk
Currently, the Azure data source defaults to using /dev/sdb for
ephemeral0. If _and only if_ we detect a fabric-formatted (i.e. NTFS)
ephemeral disk, then the data source updates this default to instead
point at that ephemeral disk (which will, correctly, be
/dev/disk/cloud/azure_resource). This happens fine on every first boot,
but on subsequent boots, we don't find a fabric-formatted ephemeral disk
(because we reformatted it on first boot), so we don't update the
default, so we end up rewriting the mounts to point at /dev/sdb (which
may not be the actual location of the ephemeral disk).
Instead of defaulting to /dev/sdb, we now default to
/dev/disk/cloud/azure_resource, which is the correct location created by
udev rules.
Ec2: protect against non-dictionary in block-device-mapping.
Oracle public cloud has the string 'unavailable' in its metadata
service for 'block-device-mapping'. The change here is to return
None in device_name_to_device if that is the case.
The implementation to add ipv6 support to Ubuntu initramfs changed
(see bug 1621507). The changes here adjust to handle the new path.
Now, the ipv6 route includes using the variable 'DEVICE6' in
net6-DEVICE.conf files.
Add coverage dependency to bddeb to fix package build.
When we added coverage to test-requirements, we need to add the mapping
to package name. Without it there, bddeb complains that it cannot
translate the dependency.
Note, though, that the Makefile does not invoke nose with coverage.
So we don't actually use that dependency.
