enable sql metadata query

explode metadata key/values to their own tables/rows (based on type).
build a key string using dot notation similar to other nosql db
and filter based on that.

Blueprint: sqlalchemy-metadata-query
Related-Bug: #1093625

Change-Id: I2076e67b79448f98124a57b62b5bfed7aa8ae2ad
Merge "enable sql metadata query"