Avoid redundant bazel build (#4458)

.bazelrc

@@ -1,2 +1,4 @@
 # build config
 build --compilation_mode=opt
+build --action_env=PATH
+build --action_env=PYTHON_BIN_PATH

build.sh

@@ -121,14 +121,15 @@ else
   $PYTHON_EXECUTABLE -m pip install \
       --target=$ROOT_DIR/python/ray/pyarrow_files pyarrow==0.12.0.RAY \
       --find-links https://s3-us-west-2.amazonaws.com/arrow-wheels/9357dc130789ee42f8181d8724bee1d5d1509060/index.html
+  export PYTHON_BIN_PATH="$PYTHON_EXECUTABLE"
 
   if [ "$RAY_BUILD_JAVA" == "YES" ]; then
     bazel run //java:bazel_deps -- generate -r $ROOT_DIR -s java/third_party/workspace.bzl -d java/dependencies.yaml
-    bazel build //java:all --verbose_failures --action_env=PATH
+    bazel build //java:all --verbose_failures
   fi
 
   if [ "$RAY_BUILD_PYTHON" == "YES" ]; then
-    bazel build //:ray_pkg --verbose_failures --action_env=PYTHON_BIN_PATH=$PYTHON_EXECUTABLE
+    bazel build //:ray_pkg --verbose_failures
   fi
 fi
 

java/test.sh

@@ -9,7 +9,9 @@ ROOT_DIR=$(cd "$(dirname "${BASH_SOURCE:-$0}")"; pwd)
 
 pushd $ROOT_DIR/..
 echo "Linting Java code with checkstyle."
-bazel test //java:all --test_tag_filters="checkstyle" --action_env=PATH
+# NOTE(hchen): The `test_tag_filters` option causes bazel to ignore caches.
+# Thus, we add the `build_tests_only` option to avoid re-building everything.
+bazel test //java:all --test_tag_filters="checkstyle" --build_tests_only
 
 echo "Running tests under cluster mode."
 # TODO(hchen): Ideally, we should use the following bazel command to run Java tests. However, if there're skipped tests,