Compact all Icehouse migrations into single one

Icehouse is the first release when we're using alembic/migrations, so,
it's the initial migration creates the db from scratch.

Implements: blueprint compact-icehouse-db-migrations
Change-Id: I902656d607571fa994a82ec6deec5281bd640e3e
Add short info re testing

Page with info about existing tests added.

Partial-Implements: blueprint update-docs-icehouse

Change-Id: I23a6ac150c0d17c2b34af8888c437dc54e0fdc72
Merge "Add short info re testing"
Merge "Compact all Icehouse migrations into single one"