Add an integration test for Android rules.

Currently only building them is tested, not running them or mobile-install, but it's still a good start.

--
MOS_MIGRATED_REVID=102237496
diff --git a/compile.sh b/compile.sh
index 1b2af73..3f7a27d 100755
--- a/compile.sh
+++ b/compile.sh
@@ -161,6 +161,11 @@
 if [ $DO_TESTS ]; then
   new_step "Running tests"
   display "."
+
+  if grep -sq '^ *actual = "//:dummy"' WORKSPACE; then
+    display "$WARNING Android SDK or NDK are not set in the WORKSPACE file. Android tests will not be run."
+  fi
+
   [ -n "$JAVAC_VERSION" ] || get_java_version
   if [[ ! "${BAZEL_TEST_FILTERS-}" =~ "-jdk8" ]] \
       && [ "8" -gt ${JAVAC_VERSION#*.} ]; then