use cassandra contact points provided via settings

[hliu9]

Description

Use settings parameter contactPoints for cassandra client options if provided.

This was a fairly trivial change, so UT was not modified... please suggest otherwise. thanks!

Related issues

If settings.contactPoints has been provided, the clientOptions is initialized without any hosts.

Checklist

• [ ] New tests added or existing tests modified to cover all changes
• [x] Code conforms with the style guide

[shenghu]

@dhmlau @virkt25 @jannyHou I think this can be merged. Do you have objection?

[shenghu]

@dhmlau this is small change. I think it is fine to merge. https://github.com/strongloop/loopback-connector-cassandra/issues/74 will add test.