add support for cluster mode (#42)

new 'cluster_client' add to support cluster mode.
the new client use CLUSTER_SLOTS command to retrive the
key-->node mapping, create separate connection fot each node,
and send the commands to the appropriate connection according
to hash calculation.

Makefile.am

@@ -25,6 +25,8 @@ memtier_benchmark_CPPFLAGS = $(LIBEVENT_CFLAGS)
 memtier_benchmark_SOURCES = \
 	memtier_benchmark.cpp memtier_benchmark.h \
 	client.cpp client.h \
+	cluster_client.cpp cluster_client.h \
+	shard_connection.cpp shard_connection.h connections_manager.h \
 	JSON_handler.cpp JSON_handler.h \
 	protocol.cpp protocol.h \
 	obj_gen.cpp obj_gen.h \

README.md

@@ -9,6 +9,7 @@ memtier_benchmark is a command line utility developed by Redis Labs (formerly Ga
  * Read:Write ratio
  * Random and sequential key name pattern policies
  * Random or ranged key expiration
+ * Redis cluster
  * ...and much more
 
 Read more at:
@@ -73,6 +74,13 @@ On recent Ubuntu versions, simply install all prerequisites as follows:
 ```
 
 
+### Cluster mode
+
+In case where there is some asymmetry between the redis nodes, and user set
+the number of total requests with sequential key pattern options, it might be
+gaps in the generated keys.
+
+
 ### Building and installing
 
 After downloading the source tree, use standard autoconf/automake commands::