install-chef-suse: Update bc-template-provisioner.json only when needed
install-chef-suse: Update bc-template-provisioner.json only when needed

We should only run bc-provisioner-json.rb if /root/.ssh/authorized_keys
exists. Otherwise, even if it doesn't exist, it will output a json file
which will be different than the original file.

Thanks to Bernhard M. Wiedemann for spotting this!

SUSE-Cloud/crowbar,mmnelemane/crowbar,mmnelemane/crowbar,rhafer/crowbar,aspiers/crowbar,toabctl/crowbar,rsalevsky/crowbar,vwallfahrer/crowbar,toabctl/crowbar,rhafer/crowbar,crowbar/crowbar,nkrinner/crowbar,tserong/crowbar,nkrinner/crowbar,SUSE-Cloud/crowbar,MaximilianMeister/crowbar,MaximilianMeister/crowbar,aplanas/crowbar,rsalevsky/crowbar,dirkmueller/crowbar,vwallfahrer/crowbar,rhafer/crowbar,aspiers/crowbar,tserong/crowbar,dirkmueller/crowbar,aplanas/crowbar,crowbar/crowbar