Handle location/creation of container image scripts

[shall1024]

The current idea is to use build_containers.sh to build container images, once a day (maybe via a cron job), and to tag the container images by date (date '+%Y.%m.%d').

From there, our scripts (in particular, start_container.sh) would choose "today's" container image when a user runs the build scripts.

This raises two concerns:

1. When re-running build_containers.sh, new container images are only built if the Dockerfiles used to build them have changed. Therefore, the current scripts often fail because they are looking for a container image with today's date when the last container image, expectedly, was created several days ago.

We either need to reconsider the tag naming conventions, or find a way for the current scripts to handle finding the "latest date" in the list of container images.

2. Are we storing the container images on builder-00.ofa.iol.unh.edu, or are we creating a container image registry on the web?

[JSpewock]

Changed the naming convention for tags to add one tag for "latest" and then another for the date the Dockerfile was last modified. This way, the start_containers script can simply look for the latest container for that distro and we have the other tag to show the last time the image was modified. Also, we're going to avoid rebuilding new images everyday as that is fairly redundant if nothing is changing in the Dockerfile. These changes can be found on the testing branch of the fsdp_build repo.