Re: [Libguestfs] [PATCH] Improve cleanup of libguestfs handle with Sys::VirtV2V::GuestfsHandle

This change replaces all direct usage of a Sys::Guestfs object in virt-v2v with a Sys::VirtV2V::GuestfsHandle proxy object. The proxy does 3 things: * Holds handle initialisation code * Adds the ability to explicitly close the handle * Adds the ability to register a callback to be executed before close The cleanup code in Sys::VirtV2V::Config is updated to use the new callback mechanism. Additionally, the initialisation code improves handling of failure while virt-v2v is running with uid:gid == 36:36. If cleanup handlers are called in this context they can fail due to insufficient permissions. If this code dies, permissions will be restored before the die is propagated. If this code receives a user signal it will be postponed until after the code has completed.