discover: Mount with norecovery, avoid rw mount of XFS filesystems

discover: Mount with norecovery, avoid rw mount of XFS filesystems

Journaled filesytems may still write to their disk even if the disk is
mounted read only. Petitboot should avoid modifying any disks
automatically, and in mixed-endian systems this can also cause journal
operations to fail. Use the 'norecovery' option on filesystems that
support it to skip the journal replay.

Additionally, mounting an XFS filesystem as read-write in such a case
will cause the call to mount to hang indefinitely. Avoid this generally
by explicitly unmounting and (re)mounting when mounting read-write.

Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>