Make jeos_create aware of existing disk files and previous glance registrations

Make jeos_create aware of existing disk files and previous glance registrations

The user is interactively prompted for decisions to be made when:
-An existing jeos disk image is found: build a fresh JEOS?
-If fresh JEOS is chosen, continue as normal removing the files and
 existing registration if it exists.
-If no fresh JEOS is chosen: register existing JEOS with glance?
-If no registration is chosen, no action is taken.
-If registration is chosen, continues as normal without rerunning oz in the
 case of the image not being previously registered with glance.
-If the image is previously registered: delete existing JEOS in glance?
-If the user chooses to not delete existing registration, no action is taken.
-If registration deletion is chosen, the registration is deleted, rerunning
 oz is skipped, and the registration will occur.

Fixes #50

Signed-off-by: Jeff Peeler <jpeeler@redhat.com>