Add a function which executes a file at a given filesystem path. This will be used as the basis of Puppet Server's implementation of the VersionedCodeService: users will specify a path in configuration with a script which will return the code ID.
The initial version of this function should return the STDOUT of the process as String. Streaming will be investigated/implemented in a future version.
There is already some prior art of this in Puppet Server, primarily in the "execution stub" provided to Puppet. Look in to this code, see what is reusable.
Also, figure out what contract around error handling is. Do we care about STDERR? Process exit code?