Improve tests for authentication

[Alexey Palazhchenko]

We should do several things (or ensure that they are already done) to improve our authentication tests. Do one separate PR for each item, one by one:

• enable "old" authentication in all existing configurations;
• enable PostgreSQL authentication (disable trust); #784
• add matrix configurations for new authentication and dotnet/java/python examples; #771
• update examples to use stable/strict API based on the value of CLI parameters;
• add matrix configurations for stable/strict API enabled.

Tasks

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1. Improve tests for dotnet #889
   +0
2. Improve tests for Java #891
   +0
3. Improve tests for Python #890
   +0
4. Improve tests for mongo-tools #892
   +0