Support a limit on number of claims

[zorkian]

By default Marshal will claim as many as it can until it becomes unhealthy.

A user has requested the ability to put an upper bound. This is useful in the situation where you know that your consumers can never operate with more than X partitions/topics. It does put more work on the part of the client to ensure they never underprovision, but this should be fine.

cc @DrTall @basharal

[zorkian]

Moved dropbox#1