Signer app hangs if TK1 stops communicating

[cibomahto]

During ESD stress testing, if the device gets shocked while tkey-sign is running, there is some chance that it hangs at:

Sending a 128 bytes message for signing.
WARNING! This tkey-sign and signer app is built with the touch requirement removed

My guess is that the tkey fails to send 1 or more bytes as a response, and there could be a timeout on the serial read (or write) to catch this.

[quite]

I've working on this as part of getting our new watchdog in place.

[cibomahto]

Thanks- it's not a blocker since the test runner can timeout and force-restart tkey-sign if it hangs for too long :-)

[quite]

We're thinking to bring in #47