Add check on <no value> config option value for the azure input resource_manager_endpoint

[narph]

What does this PR do?

Adds a check on <no value> config option value for the azure input resource_manager_endpoint
Updates test.

Why is it important?

Seems that after some recent changes, if a value is not set for resource_manager_endpoint then the value <no value> is sent to the input config. This needs to be checked at the input level.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

Do not set a value for resource_manager_endpoint when running the azure module in filebeat, no events will be generated and logs will provide more information on the error regarding the azure env.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request #18890 updated]

• Start Time: 2020-06-04T12:33:42.737+0000

• Duration: 52 min 53 sec

Test stats 🧪

Test	Results
Failed	0
Passed	2226
Skipped	382
Total	2608

Steps errors

Expand to view the steps failures

• Name: Report to Codecov

  • Description: curl -sSLo codecov https://codecov.io/bash for i in auditbeat filebeat heartbeat libbeat metricbeat packetbeat winlogbeat journalbeat do FILE="${i}/build/coverage/full.cov" if [ -f "${FILE}" ]; then bash codecov -f "${FILE}" fi done

  • Duration: 2 min 22 sec

  • Start Time: 2020-06-04T12:55:45.039+0000

  • log

• Name: Report to Codecov

  • Description: curl -sSLo codecov https://codecov.io/bash for i in auditbeat filebeat heartbeat libbeat metricbeat packetbeat winlogbeat journalbeat do FILE="${i}/build/coverage/full.cov" if [ -f "${FILE}" ]; then bash codecov -f "${FILE}" fi done

  • Duration: 2 min 22 sec

  • Start Time: 2020-06-04T13:22:49.920+0000

  • log

[kaiyan-sheng]

Should we add documentation on <no value>?

[narph]

@kaiyan-sheng

Should we add documentation on <no value>?

I don't think so, this happens only when we ignore/don't set this configuration option in the azure filebeat module.
Instead of empty string, it is somehow translated in the azure-eventhub input to <no value>.
This seems to be a new behavior, not sure when it was introduced.