[AIRFLOW-3600] Remove dagbag from trigger

[ffinfo]

Make sure you have checked all 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-3600
  • https://issues.apache.org/jira/browse/AIRFLOW-3562

Description

Removed DagBag from trigger call

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 (not including Jira issue reference)
  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

• In case of new functionality, my PR adds documentation that describes how to use it.

Code Quality

• Passes flake8

[codecov-io]

Codecov Report

Merging #4407 into master will increase coverage by 0.45%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #4407      +/-   ##
=========================================
+ Coverage   78.14%   78.6%   +0.45%     
=========================================
  Files         204     204              
  Lines       16433   16445      +12     
=========================================
+ Hits        12842   12926      +84     
+ Misses       3591    3519      -72

Impacted Files	Coverage Δ
airflow/www/views.py	70.24% <100%> (+0.77%)	⬆️
airflow/www_rbac/views.py	73.71% <100%> (+0.93%)	⬆️
airflow/models/__init__.py	92.55% <100%> (-0.02%)	⬇️
airflow/hooks/samba_hook.py	38.88% <0%> (+38.88%)	⬆️
airflow/operators/hive_to_samba_operator.py	100% <0%> (+100%)	⬆️
airflow/operators/jdbc_operator.py	100% <0%> (+100%)	⬆️

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[Fokko]

@ffinfo can you explain the reasoning behind this PR?

[ffinfo]

@Fokko I did forgot the link in jira for this. This is part of AIRFLOW-3562

[Fokko]

Ok, thanks!

[feng-tao]

@ffinfo , @Fokko , it seems that trigger_dag test is quite flaky(test_trigger_dag_button), I have seen it fails in couples of prs(e.g: https://travis-ci.org/apache/airflow/jobs/476146347) especially on mysql ORM. Do you guys know what is happening?

[feng-tao]

@ffinfo , please let me know if you will investigate the issue. If not, I prefer to revert this change until the flaky test is fixed. What do you think @Fokko ?

[Fokko]

======================================================================
42) FAIL: test_trigger_dag_button (tests.www_rbac.test_views.TestTriggerDag)
----------------------------------------------------------------------
   Traceback (most recent call last):
    tests/www_rbac/test_views.py line 1476 in test_trigger_dag_button
      self.assertIsNotNone(run)
   AssertionError: unexpectedly None

Hmm, are you sure that this PR is the source?

[feng-tao]

@Fokko , looking at recent commit, this is the one that modifies this part of the code. And the CI is not always fails with this test(sometimes works, sometimes not). Hence I suspect this pr is the case.

And we are not sure when this pr checked in CI is broken or not, right?

[feng-tao]

another failure in https://travis-ci.org/apache/airflow/jobs/476638427 for #4436. It seems the test fails very consistently with mysql ORM.