Consider hard requirement of bash

bash provides two built ins we use today via QSH:

* `cl`, which actually runs the CL command in the current job instead of in a new job like the `system` command does.
* `liblist` which also runs in the same job instead of new ones.

As of #2639, we add ASP support, which depends on bash being installed. But, it also changes some of `runCommand` (and other places) to handle if bash is not installed, and in those cases, swapping ASPs does not work.

Should we consider adding bash as a hard requirement? If a user connects, we continue to prompt the user to set bash as their default shell, and they have two options:

1. Accept, set bash as the default shell, disconnect them and ask them to connect again (one time only)
2. Decline changing the default shell, and disconnect them until they do

Thoughts?