Fix predictable placement indexing

Fix predictable placement indexing

As noted in the bug, predictable placement is broken right now
because the %index% in the scheduler hint isn't being interpolated.
This is because the parameter was moved from overcloud.yaml to the
service-specific files, which doesn't provide the index value.

Because the Compute role's parameter is named NovaCompute... we also
have to include some backwards compatibility logic to handle the
mismatch.

Change-Id: Ibee2949fe4c6c707203d7250e2ce169c769b1dcd
Closes-Bug: 1627858