Fix AppIdleHostTest

- Add CtsDeviceAppUsageTestApp to test case list
- Due to complexity of conditions required to actually
  be inactive, test that an app IS active after launching
  it. This is more important anyways, as there would be
  a negative impact if apps were wrongly put into idle
  mode.

Bug:23016850
Change-Id: I8cd7fae7da477fe33f96cc75353ca63ad8680488
diff --git a/CtsTestCaseList.mk b/CtsTestCaseList.mk
index 0950994..b758dd4 100644
--- a/CtsTestCaseList.mk
+++ b/CtsTestCaseList.mk
@@ -83,6 +83,7 @@
     CtsDeviceOpenGl \
     CtsWifiConfigCreator \
     CtsDeviceAndProfileOwnerApp \
+    CtsDeviceAppUsageTestApp \
     CtsDeviceInfo \
     CtsDeviceOwnerApp \
     CtsDeviceTaskswitchingAppA \