add -r to make resulting device read-only

add -r to make resulting device read-only

This patch adds the ability to create targets which are read-only to
keep from accidentally modifying the newly created device.  In some cases,
mounting with -o ro still modifies the device (in the case of ext3
filesystems).  I created a small patch that will do this.  I have tested it
only to the point that using -a with or without -r produces the desired
effects.

Signed-off-by: Ritesh Raj Sarraf <rsarraf@netapp.com>
Signed-off-by: Wakko Warner <wakko@animx.eu.org>