Add pauses and log repeats to avoid issues with detecting test completion on iOS/macOS.

[freakboy3742]

On macOS and iOS, add a short pause on test startup, and repeat the output of log results at the end of the test.

The log streamer takes time to start, and can drop some lines of output; this will result in a test run that was otherwise successful to fail simply because the "test was successful" marker wasn't seen.

This is particularly problematic on pre-release Pythons, as there are no binary modules, and so the test suite runs really fast - it has often finished before the log streamer starts streaming output.

This mirrors a change made on the Toga testbed. The startup delay isn't needed there because the Toga testbed takes minutes to run, and missing the first couple of lines out output isn't critical.

A better fix would be something like beeware/briefcase#2157 - but this is an immediate workaround for test unreliability when running the testbed.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[freakboy3742]

@mhsmith FYI - I've merged this without a review because the underlying problem was causing major problems for CI of the 3.14 branch of the Apple support package.