vl.c: set NULL upon deleting handlers in qemu_set_fd_handler2()

Currently qemu_set_fd_handler2() is only setting ioh->deleted upon
deleting.  This may cause a crash when a read handler calls
qemu_set_fd_handler2() to delete handlers, but a write handler is
still invoked from main_loop_wait().  Because main_loop_wait() checks
handlers before calling, setting NULL upon deleting will protect
handlers being called if already deleted.

One example is the new threaded vnc server.  When an error occurs in
the context of a read handler, it'll releases resources and deletes
handlers.  However, because the write handler still exists, it'll be
called, and then crashes because of lack of resources.  This patch
fixes it.

Signed-off-by: Yoshiaki Tamura <tamura.yoshiaki@lab.ntt.co.jp>
Reviewed-by: Corentin Chary <corentincj@iksaif.net>
PCI: Convert pci_info() to QObject

The returned QObject is a QList of all buses. Each bus is
represented by a QDict, which has a key with a QList of all
PCI devices attached to it. Each device is represented by
a QDict.

As has happended to other complex conversions, it's hard to
split this commit as part of it are new functions which are
called by each other.

IMPORTANT: support for printing PCI bridge attached devices
is NOT part of this commit, it's going to be added by the
next commit, as it's untested.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
QMP: INCOMING_FINISHED event

QEMU is started with -S and -incoming options, the only way to determine
when the incoming migration is finished is to actively poll current QEMU
status with `query-status` QMP command.

This patch allows to wait for incoming migration completion by listening
to INCOMING_FINISHED event instead of active polling of current QEMU status.
CROC's qemu-kvm.spec