Greentea DNS tests workaround.

[tymoteuszblochmobica]

Greentea DNS tests workaround due to random NSAPI DNS bug/deadlock with Nanostack

Summary of changes

Greentea DNS tests in following sequence:

-ASYNCHRONOUS_DNS_INVALID_HOST
-ASYNCHRONOUS_DNS_TIMEOUTS
sometimes causes deadlock.

nsapi_dns_query_multiple_async block on
dns_mutex->lock();
Due to async callbacks and test specific events more detailed debugging is needed
to find root cause.

Swaping tests sequence :
-ASYNCHRONOUS_DNS_TIMEOUTS
-ASYNCHRONOUS_DNS_INVALID_HOST
or add 10 ms delay causing problem disappear.
This is temporary solution to prevent Jenkins jobs fail until root cause will be fixed.

ONME-4465 is still open to find final solution.

Impact of changes

None

Documentation

None

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Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[x] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

@SeppoTakalo
@AnttiKauppila
@michalpasztamobica

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[ciarmcom]

@tymoteuszblochmobica, thank you for your changes.
@AnttiKauppila @SeppoTakalo @michalpasztamobica @ARMmbed/mbed-os-test @ARMmbed/mbed-os-ipcore @ARMmbed/mbed-os-maintainers please review.

[mbed-ci]

Test run: SUCCESS

Summary: 5 of 5 test jobs passed
Build number : 1
Build artifacts

[mergify]

This PR does not contain release version label after merging.