Increase VirtualDisplay test timeout to 40s

Some devices take longer to display the image, due to a whole bunch of
ART related optimizations running on them. They might also have slower
CPUs which exacerbate the process. This increases the time to allow the
tests to pass reliably on such devices.

Bug: 18237120
diff --git a/tests/tests/display/src/android/display/cts/VirtualDisplayTest.java b/tests/tests/display/src/android/display/cts/VirtualDisplayTest.java
index f2f859a..872de91 100644
--- a/tests/tests/display/src/android/display/cts/VirtualDisplayTest.java
+++ b/tests/tests/display/src/android/display/cts/VirtualDisplayTest.java
@@ -57,7 +57,7 @@
     private static final int WIDTH = 720;
     private static final int HEIGHT = 480;
     private static final int DENSITY = DisplayMetrics.DENSITY_MEDIUM;
-    private static final int TIMEOUT = 10000;
+    private static final int TIMEOUT = 40000;
 
     // Colors that we use as a signal to determine whether some desired content was
     // drawn.  The colors themselves doesn't matter but we choose them to have with distinct