gracefully handle file not found

[erikj]

error from my Vagrant box, which doesn't have NFS mounts

FileNotFoundError at /ncharts/projects/MASCRAD/surface_two

[Errno 2] No such file or directory: '/net/ftp/pub/archive/iss/mascrad/gaus/surface_two'

/vagrant/ncharts/views.py in get
                        dsetvars = dset.get_variables() ...
/vagrant/ncharts/models.py in get_variables
                    return ncdset.get_variables() ...
/vagrant/ncharts/netcdf.py in get_variables
                        end_time=self.end_time) ...
/vagrant/ncharts/netcdf.py in get_files
                    return self.fileset.scan(start_time, end_time) ...
/vagrant/ncharts/fileset.py in scan
                    return self.pdir.scan(start_time, end_time) ...
/vagrant/ncharts/fileset.py in scan
                        pstat = os.stat(self.path) ...