qemu.tests: Use monitor.protocol to check the monitor type

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests: Add force eject cmd when qmp monitor is used

The old code will use the old cmd from cdrom eject test which
used the wrong device for this test.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests: Add error message check in force eject test

The monitor command may failed with different reasons. Not all of them
fit our test case.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge pull request #182 from ypu/eject_media

Bug fix for eject media