fix(issuegen): Assorted fixes, most importantly ignore veth interfaces.

- Only match interface names that start with e, these are usually
  ethernet. We use the same rule for enabling DHCP in networkd.
- Support removing interfaces!
- Add tmpfiles rule so issuegen works on usr PXE images.
Merge pull request #76 from marineam/issue

fix(issuegen): Assorted fixes, most importantly ignore veth interfaces.
fix(scripts): Log big fat deprecation warnings for addon_* scripts

These have been replaced by cloud config.
fix(virtfs): Only handle 'metadata' virtfs volume.

This has been replaced by config drive in coreos-cloudinit, those
volumes are named 'config-2'. The name 'metadata' was used by both our
QEMU wrapper script and libvirt documentation.