Add placeholder test to prevent CI failure.

Bug: 197254413
Test: atest virtualizationservice_device_test
Change-Id: I5b8490f0854a002cb6a1faea78a0f60ad14991e2
diff --git a/virtualizationservice/src/main.rs b/virtualizationservice/src/main.rs
index 018be7b..8628c01 100644
--- a/virtualizationservice/src/main.rs
+++ b/virtualizationservice/src/main.rs
@@ -65,3 +65,12 @@
     }
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    /// We need to have at least one test to avoid errors running the test suite, so this is a
+    /// placeholder until we have real tests.
+    #[test]
+    #[ignore]
+    fn placeholder() {}
+}