spark git commit: Skip building R vignettes if Spark is not built

Repository: spark Updated Branches: refs/heads/branch-2.0 b25a8e6e1 -> f14f47f07 Skip building R vignettes if Spark is not built ## What changes were proposed in this pull request? When we build the docs separately we don't have the JAR files from the Spark build in the same tree. As the Spa

spark git commit: Skip building R vignettes if Spark is not built

Repository: spark Updated Branches: refs/heads/master 17b72d31e -> 9f24a17c5 Skip building R vignettes if Spark is not built ## What changes were proposed in this pull request? When we build the docs separately we don't have the JAR files from the Spark build in the same tree. As the SparkR