Request NFS mounts in request RSpec
We need a way in request RSpecs to ask to have NFS directories (primarily user and project directories) mounted.
Some design considerations:
- Needs to explicitly state which cluster they are to be mounted from. This way, AMs can reject requests that ask to mount non-local NFS servers, and the constraint system / cluster picker can make sure that you only try to use it at the right cluster
- Should probably be per-node? If it is global, then it will be impossible to use on cross-site experiments
- Should it enumerate the specific directories to mount, or basically just say "mount home and user directories like Emulab would"? Enumerating would be more general in some sense, since it could potentially be rolled into the data store syntax or semantics. But, this would be harder (probably) to adjust for all users in the project, and the latter ('like Emulab') is honestly the main semantics we probably want to preserve, and this is presumably fairly simple to do.