Use the devnode instead of the /dev/mapper path
Use the devnode instead of the /dev/mapper path

It's a bit more proper to use the devnode, even if that means relying
on a dm method that reads "/proc/partitions".

Signed-off-by: mulhern <7b51bcf507bcd7afb72bf8663752c0ddbeb517f6@redhat.com>

mulkieran/stratisd,mulkieran/stratisd,stratis-storage/stratisd,stratis-storage/stratisd,stratis-storage/stratisd,trgill/stratisd,trgill/stratisd