zvsh: Add missing env and debug sections to nvram

These two optional sections ([env] and [debug]) are now included in the
NVRAM class, so they can be included easily in the generated nvram file.
zvsh: Expand user paths in zvm-image args

Paths supplied to --zvm-image might be specified by the user as
~/foo.tar, so these paths are expanded and converted to absolute paths.
Add [env] and [debug] sections to NVRAM tests