Feature: pengine: Support cluster-specific instance attributes based on rules

The "site" term is preserved for a per-node's attribute in a stretch cluster.
Test: pengine: Support cluster-specific instance attributes based on rules
Test: pengine: Support site-specific instance attributes based on rules for stretch cluster
Merge pull request #510 from gao-yan/cluster-site-specific-params

Support cluster-specific and site-specific instance attributes based on rules