update pool::uuid() to return a PoolUuid
update pool::uuid() to return a PoolUuid

was returning a FilesystemUuid

Signed-off-by: Todd Gill <7afbb5ba98932b8ffb9cc9e6675c4792db142529@redhat.com>

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