[core][tests] csv parser bug and unit test descriptions

[jacknagz]

to @airbnb/streamalert-maintainers

size: small

changes

• Ensure we are calling the hints option with .get(). Not every parser has a hints property, so this would throw a KeyError if a given stream is analyzing both KV and CSV data.
• Add a TestKVParser unit testing class.
• Add descriptions to unit test methods. Produces a nicer and readable output when running tests:

$ ./test/scripts/unit_tests.sh
Payload Classify CSV ... ok
Payload Classify Nested CSV ... ok
Payload Classify JSON ... ok
Payload Classify KV ... ok
Payload Classify Nested JSON ... ok
Payload Classify Nested JSON Missing Subkeys ... ok
Payload Classify JSON osquery ... ok
Payload Classify Nested JSON Generic ... ok
Payload Classify Syslog ... ok
Payload Source Mapping 1 ... ok
Payload Source Mapping 2 ... ok
Payload Record Refresh ... ok
Config Validator - Valid Config ... ok
Config Validator - No Parsers ... ok
Config Validator - No Logs ... ok
Parse CloudWatch JSON ... ok
Parse Non-nested JSON objects ... ok
Parse Cloudtrail JSON ... ok
Parse Inspec JSON ... ok
Parse Multi-layered JSON ... ok
Parse KV - 'key:value,key:value' ... ok
Helpers - In Set ... ok
Helpers - Last Hour ... ok
Rule Engine - Alert Format ... ok
Rule Engine - Basic Rule/Matcher ... ok
Rule Engine - CSV Rule ... ok
Rule Engine - KV Rule ... ok
Rule Engine - Req Subkeys ... ok
Rule Engine - Syslog Rule ... ok

Name                           Stmts   Miss  Cover
--------------------------------------------------
stream_alert.py                    1      0   100%
stream_alert/classifier.py       114      4    96%
stream_alert/config.py            42     13    69%
stream_alert/parsers.py          193      4    98%
stream_alert/pre_parsers.py       58     40    31%
stream_alert/rules_engine.py      85      0   100%
--------------------------------------------------
TOTAL                            493     61    88%
----------------------------------------------------------------------
Ran 29 tests in 0.161s

OK