cephadm: add cli option to enable logging to syslog

cephadm: add cli option to enable logging to syslog

Add the --log-dest option to cephadm. The --log-dest option can be
specified 0, 1 or more times. If unspecified, cephadm will log to
the default location, the log file. If specified one ore more times,
each instance will enable the named logging destination.
Example:

```
cephadm boostrap

cephadm --log-dest=syslog bootstrap

cephadm --log-dest=file bootstrap

cephadm --log-dest=syslog --log-dest=file bootstrap
```

Signed-off-by: John Mulligan <jmulligan@redhat.com>