Limit default sar data collection

By default the general module will scoop up all files under the
/var/log/sa directory. With some configurations this path could
contain many GB of data.

Use add_copy_spec_limit() by default for sar data and add a new
option sar.all_sar=False to allow the user to override this.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>