Combine integration tests for metrics and tracing

[nhinsch]

What does this PR do?

Speeds up the integration tests running in GitHub from ~14-15 minutes to ~10 minutes.

Previously, metrics and tracing were tested separately in the integration tests. Testing different things separately is normally a good idea, but in this context it adds a lot of time to each integration test run. So, I combined the metrics and tracing code into a single function. This cuts the number of functions to test in half.

Motivation

We want the integration tests to run as fast as possible in CI.

Additional Notes

To further accelerate the integration tests in CI, we should run the tests for the different Python runtimes (e.g. 3.7, 3.8) in parallel. To do this, we should modify our integration tests to be able to run for a single runtime. Unfortunately this will be a non-trivial change because we will also need to re-work our layer publishing and signing scripts to support releasing a layer for a single runtime in the sandbox environment. We can save this work for later.

I did update the build_layers.sh script to support this, but stopped there. I decided to leave this in place so we can pick this up in the future.

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)

[DarcyRaynerDD]

LGTM