rename DIEGO_BETA -> DIEGO_STAGE_BETA [#80165358]

Signed-off-by: Matthew Sykes <matthew.sykes@gmail.com>
don't force staging on diego when running on diego

- don't restage when running on diego

[#80165358]

Signed-off-by: Matthew Sykes <matthew.sykes@gmail.com>
remove 'required' option for diego configs [#80165358]

Signed-off-by: Johannes Petzold <jpetzold@pivotal.io>
backfill test for `stage_with_diego?`

Signed-off-by: Johannes Petzold <jpetzold@pivotal.io>
update api version spec post-merge