Build stubs against SDK and clear local variables

The stubs need to be built against the current SDK where possible and
not the internal modules.

(cherry picked from commit d41d847c83)

Bug: 30188076
Test: delete stub files and remake targets
Change-Id: I9b46a4e2be341fed7e5b33bbf1a80d88c5486ae6
Merged-In: Id724c16e56d1e8fe7f61cfafe7f11ea27e01e659

test-runner/Android.mk

@@ -69,9 +69,11 @@ LOCAL_JAVA_LIBRARIES := \
     android.test.mock.stubs \
 
 LOCAL_SOURCE_FILES_ALL_GENERATED := true
+LOCAL_SDK_VERSION := current
 
 # Make sure to run droiddoc first to generate the stub source files.
 LOCAL_ADDITIONAL_DEPENDENCIES := $(android_test_runner_api_gen_stamp)
+android_test_runner_api_gen_stamp :=
 
 include $(BUILD_STATIC_JAVA_LIBRARY)