Revert "bug #1822: delete isofiles dir on iso creation failure"

This reverts commit 7e51d3f9acdb7fbd5251d051ff06cd7d940e241d.

Reverted to apply 2fbfbee9 instead
bug #1822: delete .isofiles on error in context script
(cherry picked from commit 2fbfbee94a847e107c3f5fe8d90c77001e5379d9)