qemu: process: Don't redetect backing chain on reconnect
qemu: process: Don't redetect backing chain on reconnect

Skip purging the backing chain and redetecting it when it was not going
to change during the time we were not present.

The decision is based on the new flag which records whether there were
blockjobs running to the status XML.

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