Removed unnecessary 'whitelisted' variable in the allocator.

Review: https://reviews.apache.org/r/28662
Cleaned up the utility structs in the allocator.

Review: https://reviews.apache.org/r/28663
Updated Allocator::slaveAdded to take the total resources explicitly.

Review: https://reviews.apache.org/r/28665
Updated allocator.hpp to idiomatically use the "Process wrapper" pattern.

Review: https://reviews.apache.org/r/28666
Cleaned up the allocator method naming.

Review: https://reviews.apache.org/r/28667
Fixed a bug in the allocator's framework activation.

Review: https://reviews.apache.org/r/28668
Updated allocator to only check initialization in exposed methods.

Review: https://reviews.apache.org/r/28669