[SPARK-8495][SparkR] Add a .lintr file to validate the SparkR files and the lint-r script

[yu-iskw]

Thank Shivaram Venkataraman for your support. This is a prototype script to validate the R files.

[yu-iskw]

@shivaram Could you review it when you have time? Thanks!

[SparkQA]

Test build #35366 has finished for PR 6922 at commit 8f94680.

• This patch fails RAT tests.
• This patch merges cleanly.
• This patch adds no public classes.

[shivaram]

Could you also save the output of this to a file so that users can see the report after the script exits ? The lint-python script does something similar

[yu-iskw]

@shivaram Thank you for your feedback.

• save the result to a log file
• Add the rule to the .lintr file

[SparkQA]

Test build #35367 has finished for PR 6922 at commit 5520806.

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

[SparkQA]

Test build #35370 has finished for PR 6922 at commit c1ffe6b.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[yu-iskw]

Jenkins, test this please.

[SparkQA]

Test build #35371 has finished for PR 6922 at commit c1ffe6b.

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

[shivaram]

LGTM. Thanks @yu-iskw -- BTW we should fix the existing style issues before turning it on for Jenkins but lets discuss more on the JIRA for this.

[yu-iskw]

@shivaram Thank you for reviewing! I agree with you.