Commit 984dd8ad6add4523d93c7ce5a666a32233e02e34 makes a rebuild
with a new image go through the scheduler again to validate the
image against the instance.host (we rebuild to the same host that
the instance already lives on). This fixes the subsequent doubling
of allocations that will occur by skipping the claim process if
a policy-only scheduler check is being performed.
Closes-Bug: #1732976
Related-CVE: CVE-2017-17051
Related-OSSA: OSSA-2017-006
Change-Id: I8a9157bc76ba1068ab966c4abdbb147c500604a8