Check if fsck has been started for rootfs

In case if fsck has been started it savees 2 files in directory
'/run/initramfs':
- stamp file 'fsck-root' in case if fsck run was successful
- log file 'fsck.log' with filesystem check log

Since fsck is started on every boot it is enough to make sure we have
root file system check on initramfs stage.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>