add a few dplyr tests to cover dplyr 0.6 integration
add a few dplyr tests to cover dplyr 0.6 integration

kevinykuo/sparklyr,kevinykuo/sparklyr,rstudio/sparklyr,rstudio/sparklyr,kevinykuo/sparklyr,kevinykuo/sparklyr,rstudio/sparklyr,rstudio/sparklyr