Make xen daemon startup more robust.

Make xen daemon startup more robust.
1) make xenconsoled exit gracefully if xcs dies
2) daemonize xenstored before binding to xenstored socket
3) wait to close stdio in xenstored until we're ready to accept
connections (so that PID=`xenstored --output-pid` doesn't return until
it's ready to accept connections)
4) updates tools/misc/xend for these changes
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustycorp.com.au>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>