Allow "delayed start" in watch to diagnose hard resets

[gprossliner]

When you are running a qpyt watch command, and the device resets e.g. after an AppFota or Watchdog, we manually need to rerun the command. This has several issues:

• When (re)running watch the device will perform a soft reset, so loosing it's hard reset state, this can be mitigated by running attach, not watch.
• As soon as the device firmware has booted the entry point will run, so we always will miss some logs printed to repl.

Solution:

Implement a --delayed-start flag to watch that has the following implications:

• If there is no /usr/main.py it has no effect, as there is no automatic start script
• deploy /usr/main.py as /usr/_main.py to the board. This causes QuecPython not to run it automatically
• If we loose serial connection, try to restablish it until success or user canceled
• If we have the serial connection reestablished:
• Manually run /usr/_main.py with import example;example.run("/usr/main.py") The example package is also used in QPYcom to execute .py files manually

[gprossliner]

Additional info for socket:// based connections:

The server should signat board restarts / reenumeration with closing the TCP connection. Because that may happen during sleep cycles (see #8), we need to handle that case as well.

The client must check if a reestablished session is in the state where delayed start is needed, or just when we have a reconnection based on network / server conditions. In the latter case we don't need to run anything special, just need to resume the session on a new connection.