iperf.sh: Add warning about being potentially unreliable.
iperf.sh: Add warning about being potentially unreliable.

Sometimes it hangs trying to run the server, have not debugged
yet so not sure if some bug in our logic or the automation.

dtzWill/ipcopter,dtzWill/ipcopter,dtzWill/ipcopter,dtzWill/ipcopter,dtzWill/ipcopter,dtzWill/ipcopter