[AIRFLOW-1452] "airflow initdb" stuck forever on upgrade

[patsak]

"airflow initdb" stuck forever on upgrade

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-1452

Description

• Here are some details about my PR, including screenshots of any UI changes:
  Patch fixes problem with "airflow initdb" command hanging on migration scripts. Problem met only in case MSSQL is used as storage.

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 #2514 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2514      +/-   ##
==========================================
+ Coverage   69.99%   70.02%   +0.03%     
==========================================
  Files         146      146              
  Lines       11454    11454              
==========================================
+ Hits         8017     8021       +4     
+ Misses       3437     3433       -4

Impacted Files	Coverage Δ
airflow/jobs.py	78.04% <0%> (+0.36%)	⬆️

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[allisonwang]

@patsak Thanks for fixing this :) LGTM

[aoen]

LGTM