New tool: virt-tar

New tool: virt-tar

This adds a new tool call virt-tar which is a general purpose
archive and uploading tool.  It doesn't add any functionality
which wasn't previously possible using guestfish, but makes it
simpler to access for some users.

Examples:

 virt-tar -zx myguest /home home.tar.gz
 virt-tar -zu myguest uploadstuff.tar.gz /tmp