default networks in swarm driver

[lukemarsden]

Regarding weave on swarmkit, one intrepid user is attempting to get swarmkit working with weave net by building weave from source from my fork (pending 1.9.0) and bumped into a usability issue: weave launch sets up a local scope network called weave, the user naively (although reasonably) tries docker service create --network weave and gets Error response from daemon: network weave is not eligible for docker services

Should we consider changing the default network created by weave launch to a global one, to avoid this DX issue?

cc @brb

[bboreham]

What would you do for the people who are happily using the existing mechanism?

[bboreham]

Can we detect that Docker is running in swarmkit mode? Maybe it's reasonable to create a weave network that works in that case.

[brb]

Related to #2651.