qemu: hotplug: wait for the tray to eject only for drives with a tray
qemu: hotplug: wait for the tray to eject only for drives with a tray

Use the detected tray presence flag to trigger the tray waiting code
only if the given storage device in qemu reports to have a tray.

This is necessary as the floppy device lost it's tray as of qemu commit:

commit abb3e55b5b718d6392441f56ba0729a62105ac56
Author: Max Reitz <mreitz@redhat.com>
Date:   Fri Jan 29 20:49:12 2016 +0100

    Revert "hw/block/fdc: Implement tray status"

libvirt/libvirt,andreabolognani/libvirt,olafhering/libvirt,andreabolognani/libvirt,nertpinx/libvirt,jardasgit/libvirt,taget/libvirt,crobinso/libvirt,jardasgit/libvirt,jfehlig/libvirt,datto/libvirt,fabianfreyer/libvirt,taget/libvirt,crobinso/libvirt,andreabolognani/libvirt,zippy2/libvirt,eskultety/libvirt,zippy2/libvirt,taget/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,eskultety/libvirt,eskultety/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,datto/libvirt,crobinso/libvirt,zippy2/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,datto/libvirt,olafhering/libvirt,olafhering/libvirt,libvirt/libvirt,libvirt/libvirt,taget/libvirt,libvirt/libvirt,nertpinx/libvirt,nertpinx/libvirt,jardasgit/libvirt,andreabolognani/libvirt,datto/libvirt,jfehlig/libvirt,datto/libvirt,jfehlig/libvirt,eskultety/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,crobinso/libvirt,taget/libvirt,nertpinx/libvirt,jardasgit/libvirt,andreabolognani/libvirt,zippy2/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,eskultety/libvirt,olafhering/libvirt,VenkatDatta/libvirt