redis-benchmark AUTH command to be discarded after the first send #2150

Before change:
  ​1416263718.077019 [0 127.0.0.1:57023] "SET" "key:rand_int" "xxx"
      1416263718.077019 [0 127.0.0.1:57023] "AUTH" "test"
      1416263718.077019 [0 127.0.0.1:57023] "SET" "key:rand_int" "xxx"
      1416263718.077019 [0 127.0.0.1:57023] "AUTH" "test"
      1416263718.077019 [0 127.0.0.1:57023] "SET" "key:rand_int" "xxx"
      1416263718.077019 [0 127.0.0.1:57023] "AUTH" "test"
      1416263718.077019 [0 127.0.0.1:57023] "SET" "key:rand_int" "xxx"
      1416263718.077019 [0 127.0.0.1:57023] "AUTH" "test"
      1416263718.077019 [0 127.0.0.1:57023] "SET" "key:rand_int" "xxx"
      1416263718.077019 [0 127.0.0.1:57023] "AUTH" "test"
      1416263718.077019 [0 127.0.0.1:57023] "SET" "key:rand_int" "xxx"


After the change:

 1416266483.678809 [0 127.0.0.1:23778] "AUTH" "test"
      1416266483.678809 [0 127.0.0.1:23778] "SELECT" "1"
      1416266483.678809 [1 127.0.0.1:23778] "GET" "key:__rand_int__"
      1416266483.678809 [1 127.0.0.1:23778] "GET" "key:__rand_int__"
      1416266483.678809 [1 127.0.0.1:23778] "GET" "key:__rand_int__"
      1416266483.678809 [1 127.0.0.1:23778] "GET" "key:__rand_int__"
      1416266483.678809 [1 127.0.0.1:23778] "GET" "key:__rand_int__"
      1416266483.678809 [1 127.0.0.1:23778] "GET" "key:__rand_int__"
      1416266483.678809 [1 127.0.0.1:23778] "GET" "key:__rand_int__"
      1416266483.678809 [1 127.0.0.1:23778] "GET" "key:__rand_int__"
      1416266483.678809 [1 127.0.0.1:23778] "GET" "key:__rand_int__"
      1416266483.679809 [1 127.0.0.1:23778] "GET" "key:__rand_int__"