Refactor ECSCredentialsProvider Part 2

[waahm7]

Issue:
awslabs/mountpoint-s3#859

Description of changes:

• Supports EcsContainer as a source for STSCredentials Provider.
• Refactors the STS tests with the following:
  • Update mocked connection manager to properly trigger shutdown callbacks.
  • Update mocked connection manager to support multiple request responses.
  • Update all tests to wait for all connection managers to properly shutdown.
• Reduce the NumRetries from 8 to 3 for STS and CognitoCredentialsProvider.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 79.99%. Comparing base (40f0e92) to head (59090a3).

Files	Patch %	Lines
source/credentials_provider_profile.c	90.90%	1 Missing ⚠️

Additional details and impacted files

@@                     Coverage Diff                      @@
##           fix-sts-profile-provider     #235      +/-   ##
============================================================
+ Coverage                     79.95%   79.99%   +0.03%     
============================================================
  Files                            33       33              
  Lines                          5898     5914      +16     
============================================================
+ Hits                           4716     4731      +15     
- Misses                         1182     1183       +1     

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