dracut-lib.sh: Add det_fs() and wrap_fsck()

dracut-lib.sh: Add det_fs() and wrap_fsck()

Both functions will be used by rootfs-block and fstab-sys modules.

Both are based on code present in mount-root.sh, though few changes are
present.

det_fs:

will try to determine filesystem type for supplied device, even if it's
not auto. If fs cannot be detected, or if the detected one differs from
the supplied one - a warning is issued (so user can fix its stuff later)

wrap_fsck:

will call fsck for specific device with optionally additional
fsckoptions. The function returns fsck return value.

Signed-off-by: Michal Soltys <soltys@ziu.info>