iotests: Fix 051 output after qdev_init_nofail() removal

Commit 96927c7 replaced qdev_init_nofail() call by
isa_realize_and_unref() which has a different error
message. Update the test output accordingly.

Gitlab CI error after merging b77b5b3:
https://gitlab.com/qemu-project/qemu/-/jobs/597414772#L4375

Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200616154949.6586-1-philmd@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

tests/qemu-iotests/051.pc.out

@@ -142,7 +142,7 @@ QEMU X.Y.Z monitor - type 'help' for more information
 
 Testing: -drive if=ide
 QEMU X.Y.Z monitor - type 'help' for more information
-(qemu) QEMU_PROG: Initialization of device ide-hd failed: Device needs media, but drive is empty
+(qemu) QEMU_PROG: Device needs media, but drive is empty
 
 Testing: -drive if=virtio
 QEMU X.Y.Z monitor - type 'help' for more information
@@ -214,7 +214,7 @@ QEMU X.Y.Z monitor - type 'help' for more information
 
 Testing: -drive file=TEST_DIR/t.qcow2,if=ide,readonly=on
 QEMU X.Y.Z monitor - type 'help' for more information
-(qemu) QEMU_PROG: Initialization of device ide-hd failed: Block node is read-only
+(qemu) QEMU_PROG: Block node is read-only
 
 Testing: -drive file=TEST_DIR/t.qcow2,if=virtio,readonly=on
 QEMU X.Y.Z monitor - type 'help' for more information