acnodes need to fail gracefully in event of network failure to acserver

[zymurgic]

In the event of network failure between a booted acnode and acserver, it shouldn't mis-interpret the failure to connect to acserver as a tool-should-be-out-of-service error.
especiallly when the tool is currently in use.
it should also be able to gracefully fall back to using cached credentials, especially where it's using sdcard or eeprom card caches.

Today, this occurred when a network switch crashed and failed to forward packets), taking out both the 3d printers.

[zymurgic]

acserver has been moved to the same VLAN as the acnodes themselves, which removes one point of failure. Still reliant on working network switches, but no longer reliant (at least from a packet-forwarding perspective) on a working router/firewall. Still requires DHCP leases to be able to renew or fail gracefully; A working DNS resolver is still very useful.