Some filesystem (e.g. ZFS, and btrfs subvolumes) don't use block
devices. Should they be mounted as `/`, `find_root_block_device`
yields nothing, hence dracut will append this problematic argument
to kernel cmdline:
root=/dev/block
On a machine that employ root ZFS on LUKS, which was setup with
an OpenPGP-encrypted key file, this argument renders that machine
unbootable. Remove that `root=/dev/block` manually could boot the
machine.
Let check if that device is a block device before write down `root`
argument. This is consistent with the check for block device in
`find_block_device`.
Signed-off-by: Đoàn Trần Công Danh <congdanhqx@gmail.com>
811c814677