[SPARK-12146][SPARKR] SparkR jsonFile should support multiple input files

* ```jsonFile``` should support multiple input files, such as:
```R
jsonFile(sqlContext, c(“path1”, “path2”)) # character vector as arguments
jsonFile(sqlContext, “path1,path2”)
```
* Meanwhile, ```jsonFile``` has been deprecated by Spark SQL and will be removed at Spark 2.0. So we mark ```jsonFile``` deprecated and use ```read.json``` at SparkR side.
* Replace all ```jsonFile``` with ```read.json``` at test_sparkSQL.R, but still keep jsonFile test case.
* If this PR is accepted, we should also make almost the same change for ```parquetFile```.

cc felixcheung sun-rui shivaram

Author: Yanbo Liang <[email protected]>

Closes #10145 from yanboliang/spark-12146.

Author: yanboliang

R/pkg/NAMESPACE

@@ -267,6 +267,7 @@ export("as.DataFrame",
        "createExternalTable",
        "dropTempTable",
        "jsonFile",
+       "read.json",
        "loadDF",
        "parquetFile",
        "read.df",