xenconsoled: clean-up after all dead domains

xenconsoled: clean-up after all dead domains

xenconsoled expected domains that are being shutdown to end up in the
the DYING state and would only clean-up such domains.  HVM domains
either didn't enter the DYING state or weren't in long enough for
xenconsoled to notice.

For every shutdown HVM domain, xenconsoled would leak memory, grow its
list of domains and (if guest console logging was enabled) leak the
log file descriptor.  If the file descriptors were leaked and enough
HVM domains were shutdown, no more console connections would work as
the evtchn device could not be opened.  Guests would then block
waiting to send console output.

Fix this by tagging domains that exist in enum_domains().  Afterwards,
all untagged domains are assumed to be dead and are shutdown and
cleaned up.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>