utility methods for shutting down cloud servers
remove nodes when removing instances
remove devices when removing instances
do nothing if server is None
Merge pull request #48 from planctechnologies/gns-133

Gns 133 Deleting an instance orphans devices on canvas
Grammar fixes
Merge branch 'dev' of github.com:planctechnologies/gns3-gui into dev
Merge branch 'master' into dev
Merge pull request #160 from planctechnologies/dev

Warn when deleting cloud instance with running devices