Show long help message when defined

This fixes the help template so that if a command
includes a Long form help message that is displayed instead
of ignoring it and always showing the Short message.

Signed-off-by: Daniel Hiltgen <daniel.hiltgen@docker.com>

Author: Daniel Hiltgen

cli/cobra.go

@@ -104,7 +104,7 @@ var usageTemplate = `Usage:
 {{- if not .HasSubCommands}}	{{.UseLine}}{{end}}
 {{- if .HasSubCommands}}	{{ .CommandPath}} COMMAND{{end}}
 
-{{ .Short | trim }}
+{{if ne .Long ""}}{{ .Long | trim }}{{ else }}{{ .Short | trim }}{{end}}
 
 {{- if gt .Aliases 0}}