Alternate cleanup strategy for build tests.

[freakboy3742]

An alternate approach to #271.

Instead of pre-emptively deleting Android NDK (and other) content, clean up builds and other caches after each build. Docker builds were already being cleaned up; this gives another layer of cleanup.

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]

Based on this part of the log, it looks like we pull back 3.8GB just by cleaning up Flatpak.

[rmartin16]

As an extension of this idea, I don't think much of ~/.cache/briefcase is shared between target platform builds....but some platforms download quite a bit for the build.

[edit] and wherever the android emulator gets downloaded

[freakboy3742]

As an extension of this idea, I don't think much of ~/.cache/briefcase is shared between target platform builds....but some platforms download quite a bit for the build.

[edit] and wherever the android emulator gets downloaded

True...

We seem to have avoided the immediate problem right now; perhaps it might be worth turning this into a feature on Briefcase? We've had a suggestion of a briefcase clean command in the past; with some additional flags to hit caches and other resources, it would save us from needing to hard-code specifics into this workflow.

[freakboy3742]

beeware/briefcase#1859 is already tracking the "clean" idea; I've added more details there.

[mhsmith]

There's been at least 1 failure in this cleanup on Android:

+ rm -rf build dist
rm: cannot remove 'build/verifyapp/android/gradle/app/build/intermediates/dex/release/mergeDexRelease/classes.dex': Device or resource busy
Error: Process completed with exit code 1.

This will be because the Gradle daemon is still running, and has open references to some of the files we're trying to delete. If this happens again, it can probably be worked around by adding something like this before the rm:

cd build/*/android/gradle
./gradlew --stop