It should be possible to call put with a specific set of pillars

If a client wishes to put to a subset of pillars this should be possible through the API. The reasons for not just relying on the normal 'idempotent' behaviour of the client could be:

1. If a partial put is needed because one or more pillars are now to be of line, the client must currently wait for the identifications to timeout which can be a timeconsuming task. If some pillars are know to be unavailable by the client, there is no reason to wait for the identification timeout for these.
2. A completion of a previous partial put can currently be accomplished by leveraging the current idem-potent behaviour of the put client, but will still cause the identification to be sent to the already populated pillars, which will then sent 'duplicate-failure' responses. This can be avoided by the client if a put for specific pillars is available.

• Last, it would be possible to create more robust specific pillar tests, if the test didn't depend on the availability of all pillars for put operations.