[AIRFLOW-1085] Allow the spark_home, driver_memory, and java_class to be passed to the SparkSubmitOperator

[camshrun]

Dear Airflow maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• My PR addresses the following Airflow JIRA issues and references them in the PR title.
  • https://issues.apache.org/jira/browse/AIRFLOW-1085

Description

• Adds the ability to pass the Spark home, driver memory, and Java main class to the SparkSubmitOperator.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:
  Adds:
• contrib.hooks.spark_submit_hook.TestSparkSubmitHook.test_submit_cmd
  Modifies:
• contrib.hooks.spark_submit_hook.TestSparkSubmitHook.test_build_command
• contrib.operators.spark_submit_operator.TestSparkSubmitOperator.test_execute

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"

[codecov-io]

Codecov Report

Merging #2207 into master will increase coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2207      +/-   ##
==========================================
+ Coverage    67.5%   67.64%   +0.13%     
==========================================
  Files         142      134       -8     
  Lines       10845    10737     -108     
==========================================
- Hits         7321     7263      -58     
+ Misses       3524     3474      -50

Impacted Files	Coverage Δ
airflow/__init__.py	75.6% <0%> (-3.94%)	⬇️
airflow/macros/__init__.py
airflow/utils/__init__.py
airflow/www/utils.py
airflow/executors/__init__.py
airflow/api/__init__.py
airflow/hooks/__init__.py
airflow/operators/__init__.py
airflow/task_runner/__init__.py
airflow/jobs.py	73.35% <0%> (+0.41%)	⬆️
... and 1 more

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