Consider doing an internal retry if reservation and etc. operations fail due to 409 conflict.

A reservation request may return 409 Conflict:

https://github.com/apache/mesos/blob/261d6ef497383795557aaca5dce426b4482eabea/src/master/http.cpp#L4026

It is due to the inherent race between the master and allocator actor. As illustrated here:

https://github.com/apache/mesos/blob/261d6ef497383795557aaca5dce426b4482eabea/src/master/allocator/mesos/hierarchical.cpp#L992-L1008

This is not ideal and should be rare. However, it is hard for users to grasp this error. It seems to be beneficial for Mesos to retry the reservation operation internally for the user.