Fix flag completion

The flag completion functions should be stored on their cmd struct and
not the root cmd. Using the root cmd does not work when you create the
cmd and add flags before you join this cmd struct to your parent command.

Fixes spf13#1437

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

completions.go

@@ -101,14 +101,13 @@ func (c *Command) RegisterFlagCompletionFunc(flagName string, f func(cmd *Comman
 		return fmt.Errorf("RegisterFlagCompletionFunc: flag '%s' does not exist", flagName)
 	}
 
-	root := c.Root()
-	if _, exists := root.flagCompletionFunctions[flag]; exists {
+	if _, exists := c.flagCompletionFunctions[flag]; exists {
 		return fmt.Errorf("RegisterFlagCompletionFunc: flag '%s' already registered", flagName)
 	}
-	if root.flagCompletionFunctions == nil {
-		root.flagCompletionFunctions = map[*pflag.Flag]func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective){}
+	if c.flagCompletionFunctions == nil {
+		c.flagCompletionFunctions = map[*pflag.Flag]func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective){}
 	}
-	root.flagCompletionFunctions[flag] = f
+	c.flagCompletionFunctions[flag] = f
 	return nil
 }
 
@@ -402,7 +401,7 @@ func (c *Command) getCompletions(args []string) (*Command, []string, ShellCompDi
 	// Find the completion function for the flag or command
 	var completionFn func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective)
 	if flag != nil && flagCompletion {
-		completionFn = c.Root().flagCompletionFunctions[flag]
+		completionFn = finalCmd.flagCompletionFunctions[flag]
 	} else {
 		completionFn = finalCmd.ValidArgsFunction
 	}