[Backport 2.x] Default discovery-ec2 region to none.

[opensearch-trigger-bot]

Backport f27172b from #7969.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/17152/
• CommitID: c03999d
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[kotwanikunal]

> Task :server:test

REPRODUCE WITH: ./gradlew ':server:test' --tests "org.opensearch.cluster.coordination.CoordinatorTests.testUnresponsiveLeaderDetectedEventually" -Dtests.seed=162694DEF7CDB844 -Dtests.security.manager=true -Dtests.jvm.argline="-XX:TieredStopAtLevel=1 -XX:ReservedCodeCacheSize=64m" -Dtests.locale=es-CU -Dtests.timezone=MST7MDT -Druntime.java=17

org.opensearch.cluster.coordination.CoordinatorTests > testUnresponsiveLeaderDetectedEventually FAILED
    java.lang.AssertionError: node0 has applied its state 
    Expected: <8L>
         but: was <7L>
        at __randomizedtesting.SeedInfo.seed([162694DEF7CDB844:6C4F939E12DF7B55]:0)
        at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
        at org.junit.Assert.assertThat(Assert.java:964)
        at org.opensearch.cluster.coordination.AbstractCoordinatorTestCase$Cluster.stabilise(AbstractCoordinatorTestCase.java:578)
        at org.opensearch.cluster.coordination.CoordinatorTests.testUnresponsiveLeaderDetectedEventually(CoordinatorTests.java:568)

[kotwanikunal]

> Task :server:test

REPRODUCE WITH: ./gradlew ':server:test' --tests "org.opensearch.cluster.coordination.CoordinatorTests.testUnresponsiveLeaderDetectedEventually" -Dtests.seed=162694DEF7CDB844 -Dtests.security.manager=true -Dtests.jvm.argline="-XX:TieredStopAtLevel=1 -XX:ReservedCodeCacheSize=64m" -Dtests.locale=es-CU -Dtests.timezone=MST7MDT -Druntime.java=17

org.opensearch.cluster.coordination.CoordinatorTests > testUnresponsiveLeaderDetectedEventually FAILED
    java.lang.AssertionError: node0 has applied its state 
    Expected: <8L>
         but: was <7L>
        at __randomizedtesting.SeedInfo.seed([162694DEF7CDB844:6C4F939E12DF7B55]:0)
        at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
        at org.junit.Assert.assertThat(Assert.java:964)
        at org.opensearch.cluster.coordination.AbstractCoordinatorTestCase$Cluster.stabilise(AbstractCoordinatorTestCase.java:578)
        at org.opensearch.cluster.coordination.CoordinatorTests.testUnresponsiveLeaderDetectedEventually(CoordinatorTests.java:568)

Does not fail on main with the same seed.

[dblock]

@kotwanikunal for flaky tests, look for an existing, otherwise open a new issue, I just did #7973

[kotwanikunal]

#7973

I was trying to figure out if the test is actually flaky or is it this change/branch which is causing the failure :)
Usually retrying with the same seed makes it fail, and then we raise an issue.
In this case, main does not fail with the same seed and I just tested 2.x, which fails.
Something missing or additional in 2.x.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      3 org.opensearch.search.SearchWeightedRoutingIT.testStrictWeightedRoutingWithCustomString
      1 org.opensearch.cluster.routing.allocation.decider.MockDiskUsagesIT.testRerouteOccursOnDiskPassingHighWatermark

• URL: https://build.ci.opensearch.org/job/gradle-check/17154/
• CommitID: c03999d
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Merging #7971 (c03999d) into 2.x (3df1733) will decrease coverage by 0.07%.
The diff coverage is 83.33%.

@@             Coverage Diff              @@
##                2.x    #7971      +/-   ##
============================================
- Coverage     70.61%   70.55%   -0.07%     
+ Complexity    56566    56544      -22     
============================================
  Files          4681     4681              
  Lines        268060   268062       +2     
  Branches      39656    39657       +1     
============================================
- Hits         189301   189129     -172     
- Misses        62438    62662     +224     
+ Partials      16321    16271      -50     

Impacted Files	Coverage Δ
...rg/opensearch/discovery/ec2/AwsEc2ServiceImpl.java	89.06% <75.00%> (-1.27%)	⬇️
...rg/opensearch/discovery/ec2/Ec2ClientSettings.java	98.50% <100.00%> (ø)

... and 472 files with indirect coverage changes