qemu: block commit: Don't overwrite error when rolling back disk labels
qemu: block commit: Don't overwrite error when rolling back disk labels

Calls to qemuDomainDiskChainElementPrepare resets the original error,
thus we need to save it in the cleanup path of qemuDomainBlockCommit.

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