edx_service updates

Add a key prefix to the config model.

Add a prefix from the hostname.  If building images, this will be the hostname
of the machine that the image is based on.  If running in a rolling fashion,
this will give each machine its own cache.

Update the ad-hoc-reporting mongo script.

If the cluster has a hidden secondary prefer that over a regular secondary.

Feanil/mongo 3 0 role update

sitespeed terraform pipeline fix perms