CameraITS: report skipped tests

Add skip_unless method to its.caps to exit a test with a return code
if the test is skipped.

Bug: 17994909

Change-Id: Ic6619c4219490160c638951351ee63170e3e7f6e
diff --git a/apps/CameraITS/tests/scene1/test_tonemap_sequence.py b/apps/CameraITS/tests/scene1/test_tonemap_sequence.py
index 7af51c5..435528a 100644
--- a/apps/CameraITS/tests/scene1/test_tonemap_sequence.py
+++ b/apps/CameraITS/tests/scene1/test_tonemap_sequence.py
@@ -31,10 +31,8 @@
 
     with its.device.ItsSession() as cam:
         props = cam.get_camera_properties()
-        if (not its.caps.manual_sensor(props) or
-            not its.caps.manual_post_proc(props)):
-            print "Test skipped"
-            return
+        its.caps.skip_unless(its.caps.manual_sensor(props) and
+            its.caps.manual_post_proc(props))
 
         sens, exp_time, _,_,_ = cam.do_3a(do_af=False,get_results=True)