We already check for SDKs in a lot of places, but the Gradle sdk-manager-plugin installs to ~/.android-sdk, so we should also add that to our list of places to look for installed SDKs.

That way, people can build an APK in one job, with an Android project which is using that Gradle plugin (i.e. the SDK will be installed to ~/.android-sdk), then have a separate emulator-only job which will manage to automatically download the required platforms, without having to manually point to that auto-installed SDK.