After a baremetal instance is deleted, and its allocation is removed
in placement, the ironic node might start cleaning. Eventually nova
will notice and update the inventory to be reserved.
During this window, a new instance may have already picked this
ironic node.
When that race happens today the build fails with an error:
"Failed to reserve node ..."
This change tries to ensure the remaining alternative hosts are
attempted before aborting the build.
Clearly the race is still there, but this makes it less painful.
Related-Bug: #1974070
Change-Id: Ie5cdc17219c86927ab3769605808cb9d9fa9fa4d
John Garbutt
8a476061c5