Don't log passwords on start

[jvassev]

The two passwords configurable as flags (for infoblox and dyn) are
masked now and not logged.

[hjacobs]

Thanks!

[linki]

@jvassev Thanks for spotting and fixing this!

It works but how about this approach: Add a String() method to the Config struct that pretty-prints the config data similar to now but leaves out the offending fields. This way the concern about hiding fields is close to the struct itself and main.go can be left unchanged.

[jvassev]

@linki good suggestion, looks a lot cleaner now. String() still uses %+v on a copy to skip a boring implementation.

[linki]

Thanks @jvassev