API: Tweak virDomainOpenGraphics to return fd directly

Let's fix this before we bake in a painful API.  Since we know
that we have exactly one non-negative fd on success, we might
as well return the fd directly instead of forcing the user to
pass in a pointer.  Furthermore, I found some memory and fd
leaks while reviewing the code - the idea is that on success,
libvirtd will have handed two fds in two different directions:
one to qemu, and one to the RPC client.

* include/libvirt/libvirt.h.in (virDomainOpenGraphicsFD): Drop
unneeded parameter.
* src/driver.h (virDrvDomainOpenGraphicsFD): Likewise.
* src/libvirt.c (virDomainOpenGraphicsFD): Adjust interface to
return fd directly.
* daemon/remote.c (remoteDispatchDomainOpenGraphicsFd): Adjust
semantics.
* src/qemu/qemu_driver.c (qemuDomainOpenGraphicsFD): Likewise,
and plug fd leak.
* src/remote/remote_driver.c (remoteDomainOpenGraphicsFD):
Likewise, and plug memory and fd leak.

Signed-off-by: Eric Blake <eblake@redhat.com>

include/libvirt/libvirt.h.in

@@ -5401,7 +5401,6 @@ int virDomainOpenGraphics(virDomainPtr dom,
 
 int virDomainOpenGraphicsFD(virDomainPtr dom,
                             unsigned int idx,
-                            int *fd,
                             unsigned int flags);
 
 int virDomainInjectNMI(virDomainPtr domain, unsigned int flags);