Add getOptions to pool_master

[grantcarthew]

Hi @neumino,

This is a simple change so I can access the options here:
https://github.com/grantcarthew/node-rethinkdb-job-queue/blob/master/src/queue-db.js#L13-L16

The job queue supports passing a rethinkdbdash object, in which case the db, host, port etc is unknown.
At the moment I am reading the values using:

q._host = q.r._poolMaster._options.host

With this pull request I can change it to something like:

q._host = q.r.getPoolMaster().getOptions().host

Thanks mate.

[grantcarthew]

Where would you want tests created @neumino ?