Decouple heat-plugin and allocation-pool parameters

service.runtest.tempest.neutron class contains subnet pool which
isn't supported in case of opencontrail environments. Heat
specific parameters can be placed in separate class, and class
with subnet pool can be added in model on cluster level.
Closes-bug: PROD-27115 (PROD:27115)

Change-Id: I1cce149a8e69bec6355643cff112c4da5cb013c8
3 files changed