Implement connectivity validations

[craiganderson]

Validate connection to the internet on all defined nodes
Validate connection to upstream DNS servers on all defined nodes
Validate connection to upstream NTP servers on all defined nodes
Validate connection to all environment routers/gateways on all defined nodes
Validate node-to-node connections (i.e. make sure each defined node can talk to every other node)
Validate connection and certificates for all upstream resources - e.g., all defined docker image repository locations, artifactory, github/gerrithub.io/review.openstack.org, etc.