Add ability to fully customize tests in *_{ui,unit}_test_suite macros

[brentleyjones]

Some example use cases:

• Changing how the targets are named after the runner (e.g. 18.1_UnitTests instead of UnitTests_random_runner_18.1)
• Setting per-target env, exec_properties, tags, etc.

[brentleyjones]

An alternative would be exposing the two inner rules and having people do this themselves.