Update namespace to devicefarmer

Signed-off-by: Karol Wrótniak <karol.wrotniak@droidsonroids.pl>

Bumps alpine from 3.6 to 3.12.0.

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Make things build again.

Thanks to @alexislg2 for the motivation. Fixes #6, #5, #7.

Update README.md

Use the SDK tools to install ADB, since it's no longer available in a bundle. Image size goes up but we gain access to the rest of the platform-tools/ and tools/.

Remove default ENTRYPOINT for easier debuggability. Run CMD in a shell so that we don't need a wrapper script for it.

The format of the pregenerated keys was incorrect, causing devices to ask for the key every time. This time the keys have been generated with ADB itself.