PT-2236 - pt-secure-collect, pt-pg-summary do not follow PT standard (#652)

* PT-2236 - pt-secure-collect, pt-pg-summary do not follow PT standard for option --version

- Redirected UsageWriter to os.Stdout for kingpin, so --version output
  goes to STDOUT, not to STDERR
- Adjusted text, printed by the --version flag
- Added test cases to check how --version flag works
- Adjusted test cases, so they use TOOLNAME constant

* PT-2236 - pt-secure-collect, pt-pg-summary do not follow PT standard for option --version

Run go mod tidy as requested by Artem Gavrilov

* PT-2236 - pt-secure-collect, pt-pg-summary do not follow PT standard for option --version

Renamed const TOOLNAME to toolname to follow Go coding standards

src/go/pt-mongodb-summary/main_test.go

@@ -101,7 +101,7 @@ func TestParseArgs(t *testing.T) {
 		want *cliOptions
 	}{
 		{
-			args: []string{TOOLNAME}, // arg[0] is the command itself
+			args: []string{toolname}, // arg[0] is the command itself
 			want: &cliOptions{
 				Host:               DefaultHost,
 				LogLevel:           DefaultLogLevel,
@@ -112,7 +112,7 @@ func TestParseArgs(t *testing.T) {
 			},
 		},
 		{
-			args: []string{TOOLNAME, "zapp.brannigan.net:27018/samples", "--help"},
+			args: []string{toolname, "zapp.brannigan.net:27018/samples", "--help"},
 			want: nil,
 		},
 	}