gradle start of sync-gateway fails on Windows/Ubuntu, prevents building

The recent change with adding gradle starting sync-gateway failed when I was running an event where some attendees were trying the Android mini-hack. Users on Windows and Ubuntu couldn't build the project since the sync-gateway built in download/run would fail. I know the build file seems like it shouldn't do this, but it does. Was it tested on those platforms?

Start with the Gradle build file and reproduce the sync-gateway download/run step in the Android mini-hack on Windows and Ubuntu. Investigate why that step fails on those platforms; done means the project builds successfully on both operating systems.

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