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.