java dependencies test -s -> use test -d

Summary:
To correct a build process where the JAVA_TEST_LIBDIR is a symlink to a cache directory.

Test -s (size 0) on symlinks returns true, resulting in a mkdir over the top of the symlink resulting in failure.

As a solution -d checks if it is a directory (or the symlink refers to a directory), which works in the case of real directories and symlinks to directories.

Trivial I know but it was really easy for me to use a symlink here to prevent frequent downloads in a CI environment.

Thanks for your consideration.
Closes https://github.com/facebook/rocksdb/pull/1917

Differential Revision: D4612263

Pulled By: siying

fbshipit-source-id: 4d458f8e1760068cdd6b5eae4bce6e12c400df41

java/Makefile

@@ -197,7 +197,7 @@ column_family_sample: java
 	$(AM_V_at)@rm -rf /tmp/rocksdbjni
 
 resolve_test_deps:
-	test -s "$(JAVA_TEST_LIBDIR)" || mkdir -p "$(JAVA_TEST_LIBDIR)"
+	test -d "$(JAVA_TEST_LIBDIR)" || mkdir -p "$(JAVA_TEST_LIBDIR)"
 	test -s "$(JAVA_JUNIT_JAR)" || cp $(MVN_LOCAL)/junit/junit/4.12/junit-4.12.jar $(JAVA_TEST_LIBDIR) || curl -k -L -o $(JAVA_JUNIT_JAR) http://search.maven.org/remotecontent?filepath=junit/junit/4.12/junit-4.12.jar
 	test -s "$(JAVA_HAMCR_JAR)" || cp $(MVN_LOCAL)/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar $(JAVA_TEST_LIBDIR) || curl -k -L -o $(JAVA_HAMCR_JAR) http://search.maven.org/remotecontent?filepath=org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar
 	test -s "$(JAVA_MOCKITO_JAR)" || cp $(MVN_LOCAL)/org/mockito/mockito-all/1.10.19/mockito-all-1.10.19.jar $(JAVA_TEST_LIBDIR) || curl -k -L -o "$(JAVA_MOCKITO_JAR)" http://search.maven.org/remotecontent?filepath=org/mockito/mockito-all/1.10.19/mockito-all-1.10.19.jar