Cleanup context store interfaces

This remove the term "context" from context store interfaces, to make
them more concise

Signed-off-by: Simon Ferquel <simon.ferquel@docker.com>

cli/command/context/list.go

@@ -42,7 +42,7 @@ func runList(dockerCli command.Cli, opts *listOptions) error {
 		opts.format = formatter.TableFormatKey
 	}
 	curContext := dockerCli.CurrentContext()
-	contextMap, err := dockerCli.ContextStore().ListContexts()
+	contextMap, err := dockerCli.ContextStore().List()
 	if err != nil {
 		return err
 	}