tools/xenstore: allow live update only with no transaction active

tools/xenstore: allow live update only with no transaction active

In order to simplify live update state dumping only allow live update
to happen when no transaction is active.

A timeout is used to detect guests which have a transaction active for
longer periods of time. In case such a guest is detected when trying
to do a live update it will be reported and the update will fail.

The admin can then either use a longer timeout, or use the force flag
to just ignore the transactions of such a guest, or kill the guest
before retrying.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wl@xen.org>