virttest.qemu_monitor: Workaround for weird qemu monitor output

Sometimes, we might have qemu output like

'drive_image1: /usr/local/autotest/tests/virt/shared/data/images/win7-64-sp1.qcow2 (qcow2)\n
[not inserted]\n
ide0-cd0: /usr/local/autotest/tests/virt/shared/data/isos/windows/winutils.iso (raw, read-only)\n
Removable device: not locked, tray closed\n [not inserted](qemu) '

Breaking the assumption of a (qemu) prompt separated from
the rest of the output. So we have to be less exigent when
matching the prompt.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>