qemu_vm: eliminate kill_vm_only_when_paused option

The option is not necessary anymore, as we have code specific for
-no-shutdown in the graceful-shutdown code path.

Other code that needs to wait until VM is paused outside
graceful_shutdown() may simply call wait_for_shutdown() or
wait_until_paused() directly.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

openvswitch/cfg/tests.cfg

 # File reserved for test runner (./run) use, don't modify.
 include tests-shared.cfg
 
-kill_vm_only_when_paused = no
-
 qemu_binary = /usr/bin/qemu-kvm
 qemu_img_binary = /usr/bin/qemu-img
 qemu_io_binary = /usr/bin/qemu-io