Dump the schema to a file once migrations have been run

[bradfordcp]

Also add a task to load the schema from the dumped export into a clean keyspace.This would save time as migrations wouldn't need to be run when initially setting up the project. Optionally inspect the migrations table to see if the keyspace is in a state to accept the schema load.

Code Path 1: New developer spinning up on project

inv cassandra.create cassandra.load_schema

The keyspace is created and db/schema.cql will be loaded.

Code Path 2: Developer adds a migration

inv cassandra.add_migration --name add_foo_table

developer fills out the new migration file

inv cassandra.migrate

The migration file is run (along with any other migrations that have not run). The db/schema.cql file is replaced with an updated version that contains all CREATE statements that include the new migration.

[bradfordcp]

cqlsh has a command to execute a statement. A simple implementation of this could be DESC KEYSPACE keyspace_name; with the output dumped to a file.

[bradfordcp]

Schema dumping logic has been added in 489a8ec. It appears as though loading the schema will be easier if the keyspace doesn't already exists.

[bradfordcp]

Feature complete and merged in PR #8