Exclude certain tests when running azdev test

**Is your feature request related to a problem? Please describe.**
It is not really a problem, but it would be of great convenience. In our module, 'rdbms', we have quite a large number of tests that take around ~3-4 hours just for flexible servers. We run our tests in Stage whenever a backend train is deployed. However, vnets are not supported in our stage region. As a result, we always have to comment out the vnet tests in our module or run the individual test classes like azdev test , azdev test , etc. when we run the tests in Stage. We are planning to automate this in a pipeline. However, in our pipeline, we cannot comment out tests as they are directly pulling from the master branch(azure-cli) and running the tests in the build agent. As a result, even though we know that the vnet tests would fail, we have to wait for all the tests to complete . We have around 10 tests in vnet whose run is unnecessary when we are running the pipeline in Stage.

**Describe the solution you'd like**
I am looking for something like
azdev test test_rdbms_flexible_commands --live --exclude < List of TestClassNames | List of TestFunctionNames>

**Describe alternatives you've considered**
1. Manually Commenting out tests that I dont want to run everytime
2. Individually run the test classes in the file except the tests I dont want to run.

**Additional context**
We have a automated pipeline that we run regularly in our Stage environment. We just have to ignore the failures currently as there is no way I can exclude the tests to run when I automated the pipeline. I wish I had something like azdev test test_rdbms_flexible_commands --live --exclude FlexibleServerVnetMgmtScenarioTest so that I can get to see see the complete scneario for our test results