Now that dracut runs stage1 earlier, we need to store it's exit code
for later reuse. In this, the separate dracut module will just write a
flag file in /run/drakx/ to indicate that we want to re-exec /sbin/init
(after doing some symlinks and /usr bind mount) rather than run the install.

As a result there is no need to return 0x35 ('procced') so just return
0 and keep 0x35 return code for when we really do need to restart stage1
(e.g. on a fatal error). The dracut module should loop if 0x35 is
ever returned.

In order to run stage1 we now need to do things a little differently,
namely that we move the symlinking fixups into 'init' itself which we will
actually call as a kind of fake switch_root implementation to avoid
hacking dracut too much[1]. As we run stage1 during dracut's 'mount' phase
we should not do the symlink hacks so early otherwise it will mess up
the rest of the dracut initqueue processing.

Currently, the initrd's /usr is nuked and then symlinked, but to
allow for easier debugging I now just bind mount the stage2 /usr over
the top which allows us to unmount it again easily enough if we want to
go back.

We no longer touch the /bin, /sbin or /lib[64] symlinks as these are
relative and simply bind mounting /usr is enough to fix all of them.

1. This scheme will have to change if we eventually swtich to a
systemd based dracut invocation.

the "Additional Drivers floppy" is long dead

rationale: it fixes detecting if module was already loaded or not