cri: Don't use rel path for image volumes

Runc 1.1 throws a warning when using rel destination paths, and runc 1.2
is planning to thow an error (i.e. won't start the container).

Let's just make this an abs path in the only place it might not be: the
mounts created due to `VOLUME` directives in the Dockerfile.

Signed-off-by: Rodrigo Campos <rodrigoca@microsoft.com>

integration/volume_copy_up_test.go

@@ -93,7 +93,7 @@ func TestVolumeCopyUp(t *testing.T) {
 			},
 		},
 		{
-			containerPath: "C:/weird_test_dir",
+			containerPath: "/C:/weird_test_dir",
 			files: []volumeFile{
 				{
 					fileName: "weird_test_file",