monitor_testcase_functions: add 'dd' fallback to generate I/O load

When 'dt' is not available we should be falling back to call
'dd' repeatedly to generate I/O load.

References: bnc#826109

Signed-off-by: Hannes Reinecke <hare@suse.de>
monitor_testcase_4: Use correct attach command

Depending on the setup the DASDs are either minidisks or real
disks. The former cannot be attached, but need to be linked.
So identify the setup via CP Q USERID to select the correct
command.

Signed-off-by: Hannes Reinecke <hare@suse.de>
md_monitor: Clarify error messages

There are several messages 'cannot open', so we should be
clarifying the message to figure out the failing statement.

Signed-off-by: Hannes Reinecke <hare@suse.de>
monitor_testcase_8: Fixup flashcopy command

We really shouldn't hardcode device numbers here; we need
to figure out the number from the currently used devices.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Version 4.25

Signed-off-by: Hannes Reinecke <hare@suse.de>