* docs: add R example source code
* test: check if RJDBC was installed
* test: add R test scripts
* test: chmod of test_R.sh
* test: fix test_go.sh; add R sample to document
* test: add test scripts to cases.task
* test: fix errors caused by tset_python.sh and test_java.sh
* test: fix test_python.sh
* test: modify java test case and improve opentsdb-json.mdx
* test: fix test_R.sh