LTI-279: use params from broker for room handler if specified

[Mariam05]

Description
A custom 'handler_params' setting can be added to tenants in the broker via the new rake task. These params can be used in the rooms app to form the room handler. By default, if no params are specified in the broker, the app will use the 'resource_link_id' parameter to form the handler.

How to Specify Params

# The rake task first takes a tenant's uid. the second parameter must be 'handler_params', and the third parameter is a string with as many params as you like, separated by an escaped comma, as shown below:
rake db:tenants:settings:upsert[tenant_id,handler_params,"context_id\,resource_link_id"] 

# You can delete handler parameters by using the following task:
rake db:tenants:settings:delete_handler_params[tenant_uid,handler_params]

Things to Note
Ensure that you are using the correct version of the Broker that supports using handler params from the broker.
By changing the params used for the handler will change, you will lose previous instances of Rooms. They won't be deleted from the database, but rather if you launch a Room that had been previously set up, it will be launched as a new room. The major consequence of this is that any recordings in the previous room will be lost.

How to test
In the broker, specify the params you would like to use for your tenant's rooms, and then create various rooms within one course and across a couple of courses, ensuring that the rooms are unique (this can be done by simply changing the room name or description).

[jfederico]

I am going to merge it because the urgency of solving a particular problem, but the step we follow on launch to pull credentials needs to be reviewed. It should probably use this same method in the broker helper