Add 'attached' run mode

[annybs]

e.g. edge device start --attached or -a

Because CLI backgrounds Docker interactions and runtime by default, and the container name changes after every start, it can sometimes be difficult to debug a node that is having issues.

An --attached mode which tacks the node output to stdout might make it a bit easier to provide support and diagnose problems, particularly remotely.

@adamkdean Thoughts?

[annybs]

n.b. this would be primarily for diagnostic purposes, and we would never expect a user to attach stdout in normal use.