migrations API

List all migration paths (admin only)
GET /migrations
{
    "migrations": [
        {
            "id": "1111";
            "from_version_id": "1111";
            "to_version_id": "2222";
            "from_datastore": "Mysql";
            "to_datastore": "Mysql";
            "from_version_name": "5.5.31";
            "to_version_name": "5.5.32";
        },
        {
            "id": "2222";
            "from_version_id": "1111";
            "to_version_id": "3333";
            "from_datastore": "Mysql";
            "to_datastore": "Mysql-5.6";
            "from_version_name": "5.5.31";
            "to_version_name": "5.6.13";
        }
    ]
}
# do we need datastore/version names in output?
# do we need cross-datastore migrations? (eg. if "Mysql" and "Mysql-5.6" are different datastores)

Show migration path (admin only)
GET /migrations/{migration_uuid}
{
    "migration": {
        "id": "1111";
        "from_version_id": "1111";
        "to_version_id": "2222";
        "from_datastore": "Mysql";
        "to_datastore": "Mysql";
        "from_version_name": "5.5.31";
        "to_version_name": "5.5.32";
        "migration_manager": "mysql_5_5_upgrade";
        "active": True;
    }
}

Create migration path (admin only)
POST /migrations
{
    "migration": {
        "from_version_id": "1111";
        "to_version_id": "2222";
        "migration_manager": "mysql_5_5_upgrade";
        "active": True; # optional, default is True
        # any options for migration_manager?
    }
}
Response:
{
    "migration": {
        "id": "1111";
        "from_version_id": "1111";
        "to_version_id": "2222";
        "from_datastore": "Mysql";
        "to_datastore": "Mysql";
        "from_version_name": "5.5.31";
        "to_version_name": "5.5.32";
        "migration_manager": "mysql_5_5_upgrade";
        "active": True;
    }
}
# should be default migration_manager? (eg. "SimplePackageUpdater" class which just upgrades system packages)
# should it compare image_id and/or datastore_manager for two versions?

Update migration path (admin only)
PATCH /migrations/{migration_uuid}
{
    "migration": {
        "migration_manager": "mysql_5_5_upgrade_new";
        "active": False;
    }
}
Response:
{
    "migration": {
        "id": "1111";
        "from_version_id": "1111";
        "to_version_id": "2222";
        "from_datastore": "Mysql";
        "to_datastore": "Mysql";
        "from_version_name": "5.5.31";
        "to_version_name": "5.5.32";
        "migration_manager": "mysql_5_5_upgrade_new";
        "active": False;
    }
}

List available versions for migrate to
GET /instances/{instance_id}/migrations
{
    "migrations": [
        {
            "to_version_id": "2222";
            "to_datastore": "Mysql";
            "to_version_name": "5.5.32";
        },
        {
            "to_version_id": "3333";
            "to_datastore": "Mysql-5.6";
            "to_version_name": "5.6.13";
        }
    ]
}
# skip "to_" in response?

Migrate instance to different datastore version
POST /instances/{instance_uuid}
{
    "action": {
        "migrate_version": {
            "to_version_id": "2222";
            # any options for migration_manager?
        }
    }
}