qemu: hotplug: Reuse qemuHotplugDiskSourceRemove for disk backend removal
qemu: hotplug: Reuse qemuHotplugDiskSourceRemove for disk backend removal

Add code which will convert a disk definition into
qemuHotplugDiskSourceData and then reuse qemuHotplugDiskSourceRemove to
remove all the backend related objects.

This unifies the detach code as much as possible with the already
existing helpers and will allow reuse this infrastructure when changing
removable disk media.

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

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