Core: Added support for migrations to database

Currently everytime we add or remove attributes from
DB, users need to rerun the 'rake' task to recreate the
database.

This patch will make possible to update the DB schema
without executing the rake task.

The 'migrations' extension in Sequel will check the 'schema_version'
table and apply all migrations >= than the current schema.

Migrations must be prefixed with the schema number in chronological
order and they are stored in server/lib/db/migrations.
Core: Re-use deltacloud-db-migrate in the Rake task
CIMI: Add support for 'realm' in MachineTemplate

Clients can now specify the 'realm' attribute when
creating the new MachineTemplate entity. If they then use
this MachineTemplate to create a new Machine, the Machine
will be placed into that realm.
CIMI: Print warning for pending migrations

We don't want to run any migrations automatically during
Deltacloud server boot time, to give users chance to backup
data, etc.

This patch will provide a nice warning message if you start
Deltacloud and you have some pending migrations to run.
Core: The server will now exit when there are pending migrations

+ Added missing licenses to deltacloud-db-upgrade and mock_initialize