Add eng tags to sensor examples.

We want the sensor examples to be built for all Brillo eng targets.

BUG=26980523

Change-Id: I09e15d01b88d732563f5ce32cd8757d086c020a3
diff --git a/sensors_example/Android.mk b/sensors_example/Android.mk
index 3576f5a..08363d2 100644
--- a/sensors_example/Android.mk
+++ b/sensors_example/Android.mk
@@ -30,7 +30,9 @@
 # Example app that uses sensors HAL.
 include $(CLEAR_VARS)
 LOCAL_MODULE := sensors-hal-example-app
-LOCAL_MODULE_TAGS := optional
+ifdef BRILLO
+LOCAL_MODULE_TAGS := eng
+endif
 LOCAL_SRC_FILES := hal-example-app.cpp
 LOCAL_CFLAGS := -Wno-unused-parameter
 LOCAL_SHARED_LIBRARIES := libhardware
@@ -39,7 +41,9 @@
 # Example app that uses NDK sensors API.
 include $(CLEAR_VARS)
 LOCAL_MODULE := sensors-ndk-example-app
-LOCAL_MODULE_TAGS := optional
+ifdef BRILLO
+LOCAL_MODULE_TAGS := eng
+endif
 LOCAL_SRC_FILES := ndk-example-app.cpp
 LOCAL_CFLAGS := -Wno-unused-parameter
 LOCAL_SHARED_LIBRARIES := libsensor