A collection of dracut fixes

A collection of dracut fixes

- In older systems without sysroot.mount, import before dracut-mount,
  and re-enable old dracut mount hook
- rootflags MUST be present even if the administrator neglected to
  specify it explicitly
- Check that mount.zfs exists in sbindir
- Remove awk and head as (now unused) requirements, add grep, and
  install the right mount.zfs
- Eliminate one use of grep in Dracut
- Use a more accurate grepping statement to identify zfsutil in rootflags
- Ensure that pooldev is nonempty
- Properly handle /dev/sd* devices and more
- Use new -P to get list of zpool devices
- Bail out of the generator when zfs:AUTO is on the root command line
- Ignore errors from systemctl trying to load sysroot.mount, we only
  care about the output
- Determine which one is the correct initqueuedir at run time.
- Add a compatibility getargbool for our detection / setup script.
- Update dracut .gitignore files

Signed-off-by: <Matthew Thode mthode@mthode.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4558
Closes #4562