[SPARK-8808][SPARKR] Fix assignments in SparkR.

[sun-rui]

No description provided.

[SparkQA]

Test build #37222 has finished for PR 7395 at commit 88590b1.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[yu-iskw]

@sun-rui great work! Could you show us the result of lint-r?

[shivaram]

Thanks @sun-rui LGTM.

[shivaram]

@sun-rui -- I just ran dev/lint-r and it looks like there are a few more places where we need to fix assignment. Pasting the list below

cat dev/lint-r-report.log | grep "assignment" -A 1
inst/tests/test_binary_function.R:79:12: style: Use <-, not =, for assignment.
  mockFile = c("Spark is pretty.", "Spark is awesome.")
--
inst/tests/test_binaryFile.R:23:10: style: Use <-, not =, for assignment.
mockFile = c("Spark is pretty.", "Spark is awesome.")
--
inst/tests/test_rdd.R:450:12: style: Use <-, not =, for assignment.
  mockFile = c("Spark is pretty.", "Spark is awesome.")
--
inst/tests/test_rdd.R:486:12: style: Use <-, not =, for assignment.
  mockFile = c("Spark is pretty.", "Spark is awesome.")
--
inst/tests/test_textFile.R:23:10: style: Use <-, not =, for assignment.
mockFile = c("Spark is pretty.", "Spark is awesome.")
--
inst/tests/test_utils.R:122:5: style: Use <-, not =, for assignment.
  t = 4  # Override base::t in .GlobalEnv.
--
R/client.R:39:24: style: Use <-, not =, for assignment.
    sparkSubmitBinName = "spark-submit"
--
R/client.R:41:24: style: Use <-, not =, for assignment.
    sparkSubmitBinName = "spark-submit.cmd"
--
R/DataFrame.R:1331:35: style: Use <-, not =, for assignment.
                options[['path']] = path
--
R/group.R:90:18: style: Use <-, not =, for assignment.
            cols = list(...)
--
R/group.R:100:31: style: Use <-, not =, for assignment.
                    cols[[n]] = alias(cols[[n]], n)
--
R/utils.R:44:26: style: Use <-, not =, for assignment.
                keyBytes = callJMethod(obj, "_1")
--
R/utils.R:45:26: style: Use <-, not =, for assignment.
                valBytes = callJMethod(obj, "_2")

[sun-rui]

OK. I will clean them together

[sun-rui]

All reported issues of such kind are cleaned.

[SparkQA]

Test build #37310 has finished for PR 7395 at commit ce603bc.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[shivaram]

LGTM. Merging this