iotests/172: Include "info block" in test output

iotests/172: Include "info block" in test output

The additional output demonstrates we screw up when -global isa-fdc
clashes with -drive if=floppy or its sugared forms: according to "info
qtree", only the latter backend is attached, but according to "info
block", both are.  For instance:

    Testing: -fda TEST_DIR/t.qcow2 -drive if=none,file=TEST_DIR/t.qcow2.2 -global isa-fdc.driveA=none0

	      dev: isa-fdc, id ""
	        [...]
		driveA = ""
		driveB = ""
                [...]
                bus: floppy-bus.0
                  type floppy-bus
                  dev: floppy, id ""
                    unit = 0 (0x0)
--->                drive = "floppy0"
    [...]
    floppy0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
--->    Attached to:      /machine/unattached/device[15]
        Removable device: not locked, tray closed
        Cache mode:       writeback

    none0 (NODE_NAME): TEST_DIR/t.qcow2.2 (qcow2)
--->    Attached to:      /machine/unattached/device[14]
        Cache mode:       writeback

/machine/unattached/device[15] is floppy, and
/machine/unattached/device[14] is isa-fdc.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200622094227.1271650-2-armbru@redhat.com>