Add a (non-visible in UI) use_syslog attribute, defaulting to false

We don't need to have cinder use the syslog by default, but as other
barclamps have an attribute to enable this, add this here too.
Merge pull request #31 from vuntz/use-syslog

https://github.com/crowbar/barclamp-cinder/pull/31

Merged by devtool for cloudsleuth