Teach resource tracker about stashed instance types

This removes instance_type-related database queries from the
resource_tracker.

Related to blueprint no-db-compute

Change-Id: Ia5dd407181fa733cc81d3ce03edc1c06c2aae762
Make cells_api fetch stashed instance_type info

Related to blueprint no-db-compute

Change-Id: If87bdd6a29d511117ce5d58057e601a155c64959
Merge "Teach resource tracker about stashed instance types"
Merge "Make cells_api fetch stashed instance_type info"