Made rebalance --show-plan slightly more verbose and added yet another analysis for cluster balance ("zone primary").

src/java/voldemort/client/rebalance/RebalancePartitionsInfo.java
- print out hostname within plan to make it easier to read (rather than having to lookup node ID)

src/java/voldemort/utils/ClusterInstance.java
- calculate "zone primary" balance to understand which hosted partitions act as pseudo-master when zoned routing is used.
Added KeySampler and KeyVersionSampler tools as a first step towards replacing "entropy" tool. Added another argument to bulk fetch operations that specifies maxRecords so that server can fetch a subset of a partition.

src/java/voldemort/utils/KeySamplerCLI.java
- Samples keys from a cluster

src/java/voldemort/utils/KeyVersionSamplerCLI.java
- Given file that lists keys per store, samples versions from each "responsible node" for that key

src/java/voldemort/client/protocol/admin/AdminClient.java
- passed maxRecords through
- TODO for future clean up of some types

src/java/voldemort/client/protocol/pb/VAdminProto.java
- auto generated!

src/java/voldemort/server/protocol/admin/AdminServiceRequestHandler.java
- white space

src/java/voldemort/server/protocol/admin/FetchStreamRequestHandler.java
src/java/voldemort/server/protocol/admin/FetchEntriesStreamRequestHandler.java
src/java/voldemort/server/protocol/admin/FetchKeysStreamRequestHandler.java
- handle maxRecords

src/java/voldemort/server/protocol/admin/FetchPartitionKeysStreamRequestHandler.java
src/java/voldemort/server/protocol/admin/FetchPartitionEntriesStreamRequestHandler.java
- handle maxRecords
- fixed usage of skipRecords

src/java/voldemort/utils/Entropy.java
- added maxRecords

src/proto/voldemort-admin.proto
- added mac_records to protobuff definition

test/unit/voldemort/client/AdminFetchTest.java
- added maxRecords field to test
Documented correct method of compiling protobuffs by hand.