make URI,StakingAddress to be empty when reading a tmpnet after a kill -9 of the processes

[felipemadero]

Why this should be merged

Closes #2738

pkg/localnet/tmpnet.go currently assumes that when reading a tmpnet, the node fields URI, StakingAddress
will be empty if the associated nodes are not up. This is found to not be true after killing the processes with
SIGKILL.
This PR fixes this issue by adding code to fix the network metadata based on process state

How this works

How this was tested

Two cases.

Trying to stop a network with killed nodes was failling (Ref #2738)

network start
killall -9 avalanchego
network stop

Truing to start a network with killed nodes was failling

network start
killall -9 avalanchego
network start

• CI

How is this documented