libxl: domain create: Do not destroy on ao abort

libxl: domain create: Do not destroy on ao abort

If we aborted the domain creation, do not try to tear it down again
Document this.

This is a backwards-compatible API change since old libxl users will
never abort any operations.

In the current code, there is no functional change, because
ERROR_ABORTED is never generated anywhere yet.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
---
v4: ABORTED not CANCELLED.
    Always write out guest domid on completion.
    Do not trash rc with libxl__set_domain_configuration on preserve path.