cf-promises and cf-agent need sudo

Both cf-... commands failed for me until I added sudo
Error messages:
"Can't open file /var/cfengine/masterfiles/promises.cf for parsing"
and
"Couldn't find a private key (/home/vagrant/.cfagent/ppkeys/localhost.priv) - use cf-key to get one"
Merge pull request #6 from ahormann/patch-1

cf-promises and cf-agent need sudo