[luigi.contrib.external_program.ExternalProgramTask] logs_output_pattern_to_url provided

[drowoseque]

Description

Method logs_output_pattern_to_url added to ExternalProgramTask

Motivation and Context

Sometimes our external tasks do not contain url in output logs but one easily can be restored from output
For example if we run Tez Task which outputs YARN application id only
we can restore tracking url by appending a resource manager address + endpoint
That could be done by using logs_output_pattern_to_url

Have you tested this? If so, how?

I've provided unit tests for that

[drowoseque]

@honnix @Tarrasch @dlstadther could you please review this PR?

[dlstadther]

I don't see any functional change here. Please explain.

[honnix]

LGTM now.

[drowoseque]

@honnix
okay, can we go on with that?

[honnix]

@drowoseque Could you please take a look why this broke master CI? Thanks.

[drowoseque]

I see similar failures in https://travis-ci.org/spotify/luigi/jobs/618083277 but in next build this test was okay https://travis-ci.org/spotify/luigi/builds/619552243
It seems that worker_test.DynamicDependenciesWithMultipleWorkersTes.test_dynamic_dependenciest is flaky

======================================================================
FAIL: test_dynamic_dependencies (worker_test.DynamicDependenciesWithMultipleWorkersTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/spotify/luigi/test/worker_test.py", line 1066, in test_dynamic_dependencies
    self.assertTrue(time.time() - t0 < self.timeout)
AssertionError: False is not true

[drowoseque]

@honnix could you please rerun ci ?