Fix cells RPC version 1.30 compatibility with dict-based Flavors

Version 1.30 of the cells RPC API changed the client to send Flavor
objects instead of dicts. This patch fixes the manager-side compatibility
for <=1.29 clients.

Related to blueprint kilo-objects

Change-Id: Ibde9763071c9bfcc1d7631cbf3452ed0948b4a62
Merge "Fix cells RPC version 1.30 compatibility with dict-based Flavors"