Merge branch 'yuminstall' into 'master'

Install improvements (ready for future installer changes)

This change does the following
- Copies the entire ISO, not just selected files (I think we tell people to do this anyway, so we should probably do the same)
- A couple of tweaks to installing supp packs to cope with XS-REPOSITORY-LIST being absent (and only change permissions on it if actually modifying it)

Tested with jobs 1219016 (no supp pack) and 1219071 (with supp pack) - only tested on trunk becuase this code isn't used outside of trunk.

See merge request !115