There are still 2 issues with reading btrfs labels when falling back
on using btrfs-show command, rather than primary method of using the
blkid command:
1) Label is set no "none" when btrfs-show is reporting there is no
label, although it is impossible to distinguish from the case of the
label actually being set to "none".
2) The label has 2 trailing spaces appended as the regular expression
matches "Label: (btrfslabel )uuid:" rather than
"Label: (btrfslabel) uuid:" in the btrfs-show output.
Assume a label "none" means there is no label and fix the regular
expression.
