Fixes https://github.com/cloudflare/cloudflared/issues/1460.
This required fixing new `go vet` findings:
```
tunnelrpc/pogs/configuration_manager.go:99:22: non-constant format string in call to fmt.Errorf
tunnelrpc/pogs/session_manager.go:130:22: non-constant format string in call to fmt.Errorf
ingress/ingress.go:116:20: non-constant format string in call to (*github.com/rs/zerolog.Event).Msgf
ingress/origin_proxy.go:77:21: non-constant format string in call to (*github.com/rs/zerolog.Event).Msgf
cmd/cloudflared/tunnel/subcommands.go:764:31: non-constant format string in call to github.com/cloudflare/cloudflared/cmd/cloudflared/cliutil.UsageError
```