virt: make sure that we detect unknown container managers as VIRTUALIZATION_CONTAINER_OTHER

If we don't know a container manager, we should consider it as "other"
rather than as no container manager at all, to provide a somwhat useful
upgrade path.

src/basic/virt.c

@@ -400,7 +400,7 @@ int detect_container(void) {
                         goto finish;
                 }
 
-        r = VIRTUALIZATION_NONE;
+        r = VIRTUALIZATION_CONTAINER_OTHER;
 
 finish:
         cached_found = r;