generator: Set abs_builddir for old RHEL 5 which didn't have this.
generator: Set abs_srcdir for old RHEL 5 which didn't have this.
generator: Set builddir for old RHEL 5 which didn't have this.
appliance: Don't set 'rotational' on virtio-blk devices.

virtio-blk is obsolete so we don't need to bother optimizing it.
People should use virtio-scsi instead.

Also virtio-blk should choose the optimal settings itself.

This was originally added to fix this bug:
https://bugzilla.redhat.com/show_bug.cgi?id=509383
appliance: Remove dead code which (if not dead) would have set disk scheduler to noop.
appliance: Add sensible disk optimizations.

The timeout lets us read remote images without timing out.

The noop scheduler lets the host do scheduling.  This generally makes
sense for mixed workloads because the host has a global view of the
system, and often has more compute power too.