Add --fs-type option to the 'disk' and 'osd' commands

Signed-off-by: Benoît Knecht <benoit.knecht@fsfe.org>
Fix typo in exception message

Signed-off-by: Benoît Knecht <benoit.knecht@fsfe.org>
Merge pull request #85 from BenoitKnecht/master

Add --fs-type option to the 'disk' and 'osd' commands