Fixes https://github.com/flutter/flutter/issues/156456
There is a known long running test that has been bumping up against the default timeout. This adjusts the perTestTimeout for the devicelab tests to add 15 seconds to stop this from flaking.
The test is question: 82ebb74c64/dev/devicelab/test/run_test.dart (L76)
`test/run_test.dart: run.dart script prints a message after a few seconds when failing to connect (this test takes >10s)`
Refactor the framework + test harness test suites in order to reduce testing logic in test.dart and allow for later implementing package:test onto the existing tests
The refactor of both suites included in this PR because they both depended on util functions and variables that also needed to be refactored.
Part of https://github.com/flutter/flutter/issues/145482