qemu: driver: Use qemuDomainDiskByName instead of virDomainDiskByName
qemu: driver: Use qemuDomainDiskByName instead of virDomainDiskByName

Where appropriate replace the open coded call with the qemu wrapper
which already reports the error.

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Eric Blake <a9da18479c871fe903d9590822cfe2629c6a4d11@redhat.com>

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