refactor: use new-style docker management commands

This PR uses the new syntax for commands introduced in Docker 1.13, making it a bit easier to understand just what a particular command is trying to do.

This also pushes the long-form syntax for docker command flags, which are also easier to understand at a glance.

plugins/common/common.go

@@ -325,7 +325,7 @@ func VerifyAppName(appName string) (err error) {
 
 // VerifyImage returns true if docker image exists in local repo
 func VerifyImage(image string) bool {
-	imageCmd := NewShellCmd(strings.Join([]string{DockerBin(), "inspect", image}, " "))
+	imageCmd := NewShellCmd(strings.Join([]string{DockerBin(), "image", "inspect", image}, " "))
 	imageCmd.ShowOutput = false
 	return imageCmd.Execute()
 }