Removed references to os_command_line and other properties

Setting properties to an empty dictionary was leaving all the
image properties in place.  The one property that we do keep is
the image_type.  This will list the final image in the list of
images instead of snapshots.

This is a fix for bug #34
Merge pull request #35 from redhat-imaging/bug/34

Removed references to os_command_line and other properties