Avoid getting docker images when internet connection is not available

[pisuke]

In user mode, cmd/run calls the docker registry to check for latest images. If the internet connection has less priority than the interface that DAQ uses, then it is not possible to connect to the internet and DAQ fails.

Example to fix this on debian/ubuntu based systems:

# apt install ifmetric
# route -n
# ifmetric <internet_interface> 50
# route -n 

It would be better if cmd/run doesn’t have to get the docker layers when an internet connection is not available and there are already docker layers downloaded.