Monitor queues when used for rebuilds

[martinsumner]

if a queue is used for rebuild, it is important to detect the failure of the pool, and not leave the AAE system in limbo.

Pools are monitored during a rebuild, and AAE is restarted should the pool fail before the rebuild completes.

The state has been extended on riak_kv_vnode:

• tictacaae_rebuilding now has {TS, Ref} not just TS as the state during rebuild, whereby Ref is a reference of a monitor of the pool;
• there is a a list of {reference(), Fun/1} pairs, if a 'DOWN' message is received for reference(), then the riak_kv_vnode state is updated with Fun(State) (and in this case this will restart AAE and update the controller pid on State).

Changes made to riak_kv_tictacaae_cli:

• Export of function for use in testing;
• Longer pause on sys:get_state (as the aae_controller restart in parallel mode may take up to 10s as there is an outstanding snapshot on the parallel store for the rebuild).

[martinsumner]

#165

[martinsumner]

Tested in OpenRiak/riak_test#32