xentrace 2/7: Lost-records record includes currently running vcpu,

xentrace 2/7: Lost-records record includes currently running vcpu,
and tsc of first lost record.

Including the current vcpu helps us identify who's currently
running on each processor, even if we've lost records.  The tsc of the
first lost record helps us identify how much time we've spent lost,
and also when a pcpu started experiencing lost records.

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
Signed-off-by: Trolle Selander <trolle.selander@eu.citrix.com>