[SPARK-20197][SPARKR] CRAN check fail with package installation

## What changes were proposed in this pull request?

Test failed because SPARK_HOME is not set before Spark is installed.

Author: Felix Cheung <felixcheung_m@hotmail.com>

Closes #17516 from felixcheung/rdircheckincran.

R/pkg/tests/run-all.R

@@ -22,12 +22,13 @@ library(SparkR)
 options("warn" = 2)
 
 # Setup global test environment
+# Install Spark first to set SPARK_HOME
+install.spark()
+
 sparkRDir <- file.path(Sys.getenv("SPARK_HOME"), "R")
 sparkRFilesBefore <- list.files(path = sparkRDir, all.files = TRUE)
 sparkRWhitelistSQLDirs <- c("spark-warehouse", "metastore_db")
 invisible(lapply(sparkRWhitelistSQLDirs,
                  function(x) { unlink(file.path(sparkRDir, x), recursive = TRUE, force = TRUE)}))
 
-install.spark()
-
 test_package("SparkR")