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.