Add tests for gateway api.
Add tests for gateway api.

brocaar/lora-app-server,jcampanell-cablelabs/lora-app-server,jcampanell-cablelabs/lora-app-server,jcampanell-cablelabs/lora-app-server,brocaar/lora-app-server,brocaar/lora-app-server,jcampanell-cablelabs/lora-app-server,brocaar/lora-app-server