e2e: workaround for travis 10 minute no-logs timeout
e2e: workaround for travis 10 minute no-logs timeout

Travis kills builds if it doesn't see output for 10 minutes.

The end-to-end tests take that long sometimes, and doesn't print any
intermediary output.

Print a log message very 5 minutes to work around it.

FORCE_E2E=true

GoogleCloudPlatform/golang-samples,GoogleCloudPlatform/golang-samples,adamyanliev/golang-samples,adamyanliev/golang-samples,danicat/golang-samples,adamyanliev/golang-samples,GoogleCloudPlatform/golang-samples,danicat/golang-samples,danicat/golang-samples,adamyanliev/golang-samples