[AIRFLOW-1469] Don't get aws connection if connection_id is unspecified

[NielsZeilemaker]

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. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-1469

Description

• Here are some details about my PR, including screenshots of any UI changes:
  If no aws_conn_id was specified (eg aws_conn_id == None), then the get_connection method would raise an AttributeError (AttributeError: 'NoneType' object has no attribute 'upper').
  Changed the behaviour into not attempting to get a connection for an empty/unspecified conn_id

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

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 #2485 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2485      +/-   ##
==========================================
- Coverage   69.43%   69.42%   -0.01%     
==========================================
  Files         146      146              
  Lines       11351    11351              
==========================================
- Hits         7881     7880       -1     
- Misses       3470     3471       +1

Impacted Files	Coverage Δ
airflow/jobs.py	77.02% <0%> (-0.1%)	⬇️

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[bolkedebruin]

Updated tests please!

[NielsZeilemaker]

Fixed in #2532