cli-plugins: minor cleanups: use Println

- use Println to print newline instead of custom format
- suppress some errors to make my IDE and linters happier
- use res.Assert() with icmd.Expected{} where possible to make
  assertions not depend on newline / whitespace randomness
- use apiClient instead of client for the API client to
  prevent shadowing imports.
- use dockerCLI with Go's standard camelCase casing.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli-plugins/hooks/printer.go

@@ -11,8 +11,8 @@ func PrintNextSteps(out io.Writer, messages []string) {
 	if len(messages) == 0 {
 		return
 	}
-	fmt.Fprintln(out, aec.Bold.Apply("\nWhat's next:"))
+	_, _ = fmt.Fprintln(out, aec.Bold.Apply("\nWhat's next:"))
 	for _, n := range messages {
-		_, _ = fmt.Fprintf(out, "    %s\n", n)
+		_, _ = fmt.Fprintln(out, "   ", n)
 	}
 }