Updates to README.build.md and Derecho Switch

[scrasmussen]

TYPE: enhancement

KEYWORDS: README, Derecho

SOURCE: Soren Rasmussen, NCAR

DESCRIPTION OF CHANGES: Updates to README.build.md and Derecho name updates

NOTE I: changes to the testing directory scripts just change the name from Cheyenne to Derecho but don't update the files, they are old and probably won't work.

NOTE II: this PR should be squashed-and-merged

Checklist

• Closes issue #xxxx (An issue must exist or be created to be closed. The issue describes and documents the problem and general solution, the PR describes the technical details of the solution.)
• Tests added (unit tests and/or regression/integration tests)
• Backwards compatible
• Requires new files? If so, how to generate them.
• Documentation included
• Short description in the Development section of NEWS.md

[rcabell]

I made a small comment about MPI but it's not a deal-breaker. Just something to think about...