Add initialization handshake timeout

Author: fhunleth

rel/vm.args.eex

@@ -10,6 +10,10 @@
 ## break handler and possibly exiting the VM.
 +Bc
 
+## Require an initialization handshake within 10 minutes from the startup guard
+## See https://hexdocs.pm/nerves_runtime/readme.html#assisted-firmware-validation-and-automatic-revert
+-env HEART_INIT_TIMEOUT 600
+
 # Allow time warps so that the Erlang system time can more closely match the
 # OS system time.
 +C multi_time_warp