Problem: Zombie dump threads on Master (>= MySQL-5.6 version)
         that are created to server slaves which are on lower
         versions than MySQL-5.6 version are not getting killed.

Analysis: Starting from MySQL-5.6 version, Master is detecting a zombie dump
          thread only based on slave's UUID value under the assumption that
          each Slave (>= MySQL-5.6 version) will set unique UUID. In case of
          slaves which are on lower version than MySQL-5.6 version will not
          set UUID. Hence Master (>= MySQL-5.6 version) is unable to detect
          zombie dump threads that are created to serve slaves which are on
          lower versions than MySQL-5.6 version.

Fix: Master will check first if there is UUID set by Slave. If it is set,
     zombie dump thread detection happens based on UUID. If it is not set,
     zombie dump thread detection happens based on server id.