nfs: strip out Cassandra and Ceph backends

[BlaineEXE]

Do a rough job of stripping out Ceph and Cassandra backends from the codebase. This should build, and tests should pass. Documentation is updated as best as possible.

Signed-off-by: Blaine Gardner blaine.gardner@redhat.com

Description of your changes:

Which issue is resolved by this Pull Request: Resolves #

Checklist:

• [ ] Commit Message Formatting: Commit titles and messages follow guidelines in the developer guide.
• [ ] Skip Tests for Docs: Add the flag for skipping the build if this is only a documentation change. See here for the flag.
• [ ] Skip Unrelated Tests: Add a flag to run tests for a specific storage provider. See test options.
• [ ] Reviewed the developer guide on Submitting a Pull Request
• [ ] Documentation has been updated, if necessary.
• [ ] Unit tests have been added, if necessary.
• [ ] Integration tests have been added, if necessary.
• [ ] Pending release notes updated with breaking and/or notable changes, if necessary.
• [ ] Upgrade from previous release is tested and upgrade user guide is updated, if necessary.
• [ ] Code generation (make codegen) has been run to update object specifications, if necessary.