iso: Reduce verbosity on test and info calls

iso: Reduce verbosity on test and info calls

The test and info callbacks into the partition callback struct are
used by the "part list" command on the command line. That command
is used by the distro script.

With verb=1 set, "part list" thus throws a lot of warnings about
partitions it can't find when an upper layer searches for partitions.

So let's reduce verbosity to bring it to the same level of noise
as the other partition targets.

Signed-off-by: Alexander Graf <agraf@suse.de>