--secretsdir has no default value

The --secretsdir option in maxctrl has no default value which means that passing an encrypted password will not work without --secretsdir=/var/lib/maxscale/. Since the default location is usually where people set it up, having read access to it (e.g. via sudo) should automatically cause encrypted passwords to be decrypted.

This should be a safe change to do as an inability to decrypt the password will just skip the decryption and try to use it as-is.