Cleanups to use rsnapshot specific key and make Berkshelf compatible.

There are several sets of change:

* Replace white space in description clauses for Berkshelf compatibility.
* Change default key location to /etc/rsnapshot/keys/rsnapshot_dsa.
* Set SSH directory to be node variable, /etc/rsnapshot/keys by default.
* Set keyfile to be node variable, 'rsnapshot_dsa' by default
* Set key to be DSA, not RSA.
* Clean up 'command' wrapper logic, just use one legible line.
* Add 'sudo' dependency
* Add .gitignore file.