dispatcher: lower a monitor-config warning to a debug level
dispatcher: lower a monitor-config warning to a debug level

Some QXLInterface implementations might not have or succeed
with client_monitors_config(). Thus, lower warning to debug
level.

https://bugzilla.redhat.com/show_bug.cgi?id=1119220

ya-mouse/spice,fgouget/spice,freedesktop-unofficial-mirror/spice__spice,SPICE/spice,freedesktop-unofficial-mirror/spice__spice,Fantu/spice,elmarco/spice,freedesktop-unofficial-mirror/spice__spice,Fantu/spice,Fantu/spice,ya-mouse/spice,freedesktop-unofficial-mirror/spice__spice,fgouget/spice,elmarco/spice,Fantu/spice,elmarco/spice,SPICE/spice,fgouget/spice,elmarco/spice,freedesktop-unofficial-mirror/spice__spice,elmarco/spice,SPICE/spice,fgouget/spice,ya-mouse/spice