qemu_vm, aexpect, utils_misc: attempt to catch qemu in defunct state.

Add support to detect if qemu becomes <defunct> (zombie)
after it was started. If qemu is detected defunct, it will
raise virt_vm.VMStartError().

Signed-off-by: Ruda Moura <rmoura@redhat.com>
Merge pull request #1255 from ruda/qemu-defunct

qemu_vm, aexpect, utils_misc: attempt to catch qemu in defunct state.