AWS: Customize Route 53 assignment

[acr92]

Currently the Route 53 configuration in the AWS rigger script is meant for test (ref DEIS_TEST_DOMAIN).

Some users (e.g. myself) use Route 53 and would like to be able to enable/customize this (e.g. as a step during the cofiguration).

For users which don't use Route 53, the script should not attempt to assign a Route 53 DNS address.

[sgoings]

Also see: #5