virtcontainers: 9p: shares multiple devices with only one export

Use 'remap' behaviour to deal with multiple devices being shared with
a 9p export.

Fixes the following warning:

```
9p: Multiple devices detected in same VirtFS export, which might lead to file
ID collisions and severe misbehaviours on guest!
You should either use a separate export for each device shared from host or
use virtfs option 'multidevs=remap'!
```

fixes #378

Signed-off-by: Julio Montes <julio.montes@intel.com>

src/runtime/virtcontainers/qemu_arch_base.go

@@ -460,6 +460,7 @@ func generic9PVolume(volume types.Volume, nestedRun bool) govmmQemu.FSDevice {
 		MountTag:      volume.MountTag,
 		SecurityModel: govmmQemu.None,
 		DisableModern: nestedRun,
+		Multidev:      govmmQemu.Remap,
 	}
 }
 

src/runtime/virtcontainers/qemu_arch_base_test.go

@@ -329,6 +329,7 @@ func TestQemuArchBaseAppend9PVolume(t *testing.T) {
 			Path:          hostPath,
 			MountTag:      mountTag,
 			SecurityModel: govmmQemu.None,
+			Multidev:      govmmQemu.Remap,
 		},
 	}
 

src/runtime/virtcontainers/qemu_test.go

@@ -211,6 +211,7 @@ func TestQemuAddDeviceFsDev(t *testing.T) {
 			Path:          hostPath,
 			MountTag:      mountTag,
 			SecurityModel: govmmQemu.None,
+			Multidev:      govmmQemu.Remap,
 		},
 	}