blkid: escape quotes in the output

 # e2label /dev/loop0 'La"bel'
 # blkid -p /dev/loop0
 /dev/loop0: LABEL="La"bel"  ....

new version:

 /dev/loop0: LABEL="La\"bel" ....

Reported-by: Phillip Susi <psusi@ubuntu.com>
Signed-off-by: Karel Zak <kzak@redhat.com>