[Libguestfs] Create new Sys::VirtV2V::Util

These 2 patches are mostly code motion. They were prompted by an apparent augeas error in BZ 613967 which didn't display useful error message. The error seems to happen in Converter::Linux. GuestOS::RedHat had a handy function which displayed verbose augeas error messages. This function moves into the new module where it can be used by both modules. The second patch is an consequential tidy up. UserMessage moves into the new module. * [PATCH 1/2] Move augeas error reporting into new Sys::VirtV2V::Util * [PATCH 2/2] Move user_message into Sys::VirtV2V::Util