reset provider creds on every invocation

[ammokhov]

Issue #, if available:

Description of changes:

Change

This change resets provider credentials during runtime initialization even when passed in provider creds are null. Previously, when a lambda container was reused and passed in credentials were null, we would use the same credentials from the previous request.

In the extensive logging I added to verify the issue and test the fix, I also found a bug whereby every time we invoke, we add the lambda logger to the platformProxyLogger, which causes us to log any messages on that logger X number of times, where X is the number of the times the lambda container was reused. I made the 1 line change to ensure that we only log messages once.

Testing

Verified issue and tested by uploading the jar to a function on the lambda console and logging the credentials used (those log statements have been removed from this PR of course).

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