throw proper error when port is not accessible
for the regular user, this is possibly a regression.
```
ERROR Unable to start the server: Insufficient permissions to use specified port
> Please ensure MinIO binary has 'cap_net_bind_service=+ep' permissions
HINT:
Use 'sudo setcap cap_net_bind_service=+ep /path/to/minio' to provide sufficient permissions
```
minio server /data{1..4} shows an error about inability to bind a port, though
the real problem is /data{1..4} cannot be created because of the lack of
permissions.
This commit fix the behavior.
