Add support for constraints in profile

[ketan]

I'm running a swarm with nodes running on centos 7 and windows 2016 server. When I schedule a service, it usually "bounces" between various hosts because a windows container when scheduled on a linux host fails and gets re-assigned to another host until it is assigned to a windows host. Similar thing happens when a linux container is scheduled on a windows host. Depending on the number of bounces, it can take several seconds for the container to come up.

In such mixed-os swarm clusters, it is recommended that:

• each node be "tagged" with a label:
  docker node update --label-add "os=[windows|linux]"
• when scheduling a particular service, apply a constraint to run on a specific node(s):
  docker service create --constraint 'node.labels.os==windows'