Skip reset upon flashing if not needed

[flaki]

via @yyyc514:

what should happen is if the serial is there it should try and talk AVR109, if that succeeds - flash
only do a reset if the port won't talk avr109
reset is the most common scenario but it shoudlnt' be hard to do the check

[joshgoebel]

Aasking for the signature and getting "CATERINA" back or whatever the signature is would be a simple enough test.