All artifacts for iOS are universal.

Instead, require an AndroidManifest.xml and always build an APK.

Fixes #2517

Previously we were ignoring the return code and continuing.

@devoncarew

flutter start's method of finding devices to run the app on is not suitable for flutter drive.

This commit also refactors several tool services to allow mocking in unit tests.

Runs a test app and a driver test simultaneously, then stops the app.

Usage:

```
flutter drive --target=/path/to/test/app.dart
```

This command will look for `/path/to/test/app_test.dart` by
convention. We will expand into other ways of discovering tests in the
future.

This removes a step that can cause trouble.

Fixes #1904

Previously we'd always stop org.domokit.sky.shell. If an
AndroidManifest.xml exists, we'll use the activity specified in there
instead.

flutter start no longer depends on a pre-built SkyShell.apk. It builds a
new one, as long as an AndroidManifest.xml exists.

We rebuild the .apk every time either AndroidManifest.xml or
flutter.yaml changes.

fixed sub-process stdout parsing; added todos

Add a --full-restart flag to the start command that controls whether we stop the application process

SkyActivity now allows reloading application Dart code within an existing
activity.  If a SkyActivity instance is already running, then passing
--no-full-restart will restart the Dart code without killing and restarting
the SkyShell application.
(full-restart will remain the default until the engine
that supports this is rolled out)

Also remove the obsolete --poke flag

rename to printTrace(), printStatus(), and printError()

remove device type specific checks