The patch fixes some lvconvert issues (WRT mirror <-> mirror).

The patch fixes some lvconvert issues (WRT mirror <-> mirror).

The default log option for a mirror is 'disk'.  If the log
type is not explicitly stated on the command line when
converting from an X-way mirror to a Y-way mirror, 'disk'
is chosen.  So, if you have a 'core' log mirror and you
convert, your result will contain a 'disk' log.

This patch remembers what the old log type was.  If the
user is merely trying to switch the number of mirror
images, the log type is now kept the same.

There is one historical behaviour I left in place...
If you have a 2-way, core-log mirror and you use lvconvert to
specify you want a 2-way mirror - without specifying the
log type - you will get a 2-way, disk-log mirror.

Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Informal-IRC-ACK-by: agk