Replace temporary SCHEDULER_ADDRESS in Dask tutorial

[mrakitin]

https://github.com/NSLS-II/tutorial/blob/master/tutorials/Parallelize%20with%20Dask.ipynb contains the invalid scheduler address:

SCHEDULER_ADDRESS = 'ae8cfeafc5ad611e88b00021c84f1ed3-1000724570.us-east-1.elb.amazonaws.com:8786

This should be resolved before the user meeting 2019.

[danielballan]

Proposed solution:

Use AWS Route53 so make an ALIAS record at dask-scheduler.blueskyproject.io that points to the SCHEDULER_ADDRESS. When the SCHEDULER_ADDRESS changes, we can update Route53 (which propagates instantly) instead of updating (potentially several) notebooks.