KVM SR: scalability testnode integration.
KVM component: use h.r.download to download debian image.
SlapOS Stack: update buildout and h.r.download versions to use.
resiliency stack: pin old s.r.template.

Because new s.r.templare requires new Jinja2.
Resiliency: allow takeover to retry renaming until it works.
KVM SR: stop export/import if previous step failed.
KVM SR: Allow to run standalone resiliency script without testrunner.