[AIRFLOW-2563] Fix PigCliHook Python 3 string/bytes use

[jakahn]

Make sure you have checked all steps below.

JIRA

• My PR addresses the following Airflow JIRA issues and references them in the PR title. F
  • https://issues.apache.org/jira/browse/AIRFLOW-2563

Description

• This PR fixes PigCliHook's Python 2-style use of strings where Python 3 requires (or returns) a bytes-like object. It also introduces unit tests for PigCliHook, which were missing.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:
  • tests/hooks/test_pig_hook.py

Commits

• My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• No new non-test files or new functionality.

Code Quality

• Passes git diff upstream/master -u -- "*.py" | flake8 --diff

[codecov-io]

Codecov Report

Merging #3594 into master will increase coverage by 0.26%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3594      +/-   ##
==========================================
+ Coverage   76.85%   77.12%   +0.26%     
==========================================
  Files         204      204              
  Lines       15522    15522              
==========================================
+ Hits        11930    11971      +41     
+ Misses       3592     3551      -41

Impacted Files	Coverage Δ
airflow/hooks/pig_hook.py	100% <100%> (+100%)	⬆️

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[jakahn]

The failing test appears to have been a flake (Travis reports a 10 minute period of no output on an unrelated test; all tests pass on my fork).

[Fokko]

Please link to your fork instead of retriggering every time.

[jakahn]

Sure, sorry about that!

• Travis: https://travis-ci.org/jakahn/incubator-airflow
• Fork: https://github.com/jakahn/incubator-airflow

[jakahn]

Just bumping since it's been ~2 weeks

[artwr]

LGTM +1