[SPARK-17339][SPARKR][CORE] Fix some R tests and use Path.toUri in SparkContext for Windows paths in SparkR

## What changes were proposed in this pull request?

This PR fixes the Windows path issues in several APIs. Please refer https://issues.apache.org/jira/browse/SPARK-17339 for more details.

## How was this patch tested?

Tests via AppVeyor CI - https://ci.appveyor.com/project/HyukjinKwon/spark/build/82-SPARK-17339-fix-r

Also, manually,

![2016-09-06 3 14 38](https://cloud.githubusercontent.com/assets/6477701/18263406/b93a98be-7444-11e6-9521-b28ee65a4771.png)

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #14960 from HyukjinKwon/SPARK-17339.

Author: HyukjinKwon

R/pkg/inst/tests/testthat/test_mllib.R

@@ -22,6 +22,11 @@ context("MLlib functions")
 # Tests for MLlib functions in SparkR
 sparkSession <- sparkR.session(enableHiveSupport = FALSE)
 
+absoluteSparkPath <- function(x) {
+  sparkHome <- sparkR.conf("spark.home")
+  file.path(sparkHome, x)
+}
+
 test_that("formula of spark.glm", {
   training <- suppressWarnings(createDataFrame(iris))
   # directly calling the spark API
@@ -354,7 +359,8 @@ test_that("spark.kmeans", {
 })
 
 test_that("spark.mlp", {
-  df <- read.df("data/mllib/sample_multiclass_classification_data.txt", source = "libsvm")
+  df <- read.df(absoluteSparkPath("data/mllib/sample_multiclass_classification_data.txt"),
+                source = "libsvm")
   model <- spark.mlp(df, blockSize = 128, layers = c(4, 5, 4, 3), solver = "l-bfgs", maxIter = 100,
                      tol = 0.5, stepSize = 1, seed = 1)
 
@@ -616,7 +622,7 @@ test_that("spark.gaussianMixture", {
 })
 
 test_that("spark.lda with libsvm", {
-  text <- read.df("data/mllib/sample_lda_libsvm_data.txt", source = "libsvm")
+  text <- read.df(absoluteSparkPath("data/mllib/sample_lda_libsvm_data.txt"), source = "libsvm")
   model <- spark.lda(text, optimizer = "em")
 
   stats <- summary(model, 10)
@@ -652,7 +658,7 @@ test_that("spark.lda with libsvm", {
 })
 
 test_that("spark.lda with text input", {
-  text <- read.text("data/mllib/sample_lda_data.txt")
+  text <- read.text(absoluteSparkPath("data/mllib/sample_lda_data.txt"))
   model <- spark.lda(text, optimizer = "online", features = "value")
 
   stats <- summary(model)
@@ -688,7 +694,7 @@ test_that("spark.lda with text input", {
 })
 
 test_that("spark.posterior and spark.perplexity", {
-  text <- read.text("data/mllib/sample_lda_data.txt")
+  text <- read.text(absoluteSparkPath("data/mllib/sample_lda_data.txt"))
   model <- spark.lda(text, features = "value", k = 3)
 
   # Assert perplexities are equal

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -992,7 +992,7 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
 
     // This is a hack to enforce loading hdfs-site.xml.
     // See SPARK-11227 for details.
-    FileSystem.get(new URI(path), hadoopConfiguration)
+    FileSystem.getLocal(hadoopConfiguration)
 
     // A Hadoop configuration can be about 10 KB, which is pretty big, so broadcast it.
     val confBroadcast = broadcast(new SerializableConfiguration(hadoopConfiguration))
@@ -1081,7 +1081,7 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
 
     // This is a hack to enforce loading hdfs-site.xml.
     // See SPARK-11227 for details.
-    FileSystem.get(new URI(path), hadoopConfiguration)
+    FileSystem.getLocal(hadoopConfiguration)
 
     // The call to NewHadoopJob automatically adds security credentials to conf,
     // so we don't need to explicitly add them ourselves