Implement functionality to skip tests via TESTBRIDGE_TEST_ONLY env

[yushan26]

What type of PR is this?

Feature

What does this PR do? Why is it needed?
This PR implements the functionality to skip tests via TESTBRIDGE_TEST_ONLY env field. TESTBRIDGE_TEST_ONLY will expect a comma-separated list of regex expressions. A prefix '-' to the regex specifies to excluded test case matching the filter (similar to instrumentaion_filter.
For example:
To indicate tests to run all the tests except for TestFQNTaskFiler and TestTargetTaskFiler, provide the environment in go_test:
env = {"TESTBRIDGE_TEST_ONLY":"-^TestFQNTaskFiler$,-^TestTargetTaskFiler$"}

This is the opposite behavior of the existing behavior go test -run.
This is needed in order to skip flaky test cases in CI.

Which issues(s) does this PR fix?

Fixes #2785

Other notes for review

[linzhp]

Let's implement the same convention as --instrumentation_filter:

a comma-separated list of regex expressions with prefix '-' specifying excluded paths

In your example above, it should be --test_filter -^TestFQNTaskFiler$,-^TestTargetTaskFiler$

We can potentially pass something like --test_filter ^TestTask.+,-^TestTaskB$, meaning we want to only run tests with prefix TestTask, except TestTaskB.

[linzhp]

Also, add some tests to cover this feature

[linzhp]

Thank your for working on this. I am really excited to see this implemented finally!