libxl: don't set hasManagedSave when performing save

libxl: don't set hasManagedSave when performing save

libxlDoDomainSave() is used in both the save and managedsave code
paths but was unconditionally setting hasManagedSave to true on
success. As a result, undefine would fail after a non-managed
save/restore operation. E.g.

virsh define; virsh start
virsh save; virsh restore
virsh shutdown
virsh undefine
error: Refusing to undefine while domain managed save image exists

Modify libxlDoDomainSave() to take an additional parameter to
specify managed vs non-managed save, and change callers to use it.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>