REPLICATION

Problem: Corruption of one channel's relay logs + server restart is
         making few channels (good channels) to disappear.

Analysis: In create_slave_info_objects(), after reading the all the
          available channels from the repository tables, server create
          and initialize each and every channel. The logic was written
          in such a way that if there is an error while initializing
          one channel, server will skip creating other channels than
          the default one. Also when the skip-slave-start=false, server
          should start the slave threads for all the channels. But the logic
          is written in a way that if there is an error during initialization
          of a channel, it will skip starting slave threads for those
          channels which are in good condition as well.

Fix: Both problems that are explained above in the analysis section are
     fixed now. Now irrespective of errors on other channels, server will try
     to create/initialize channels that are in good condition and also
     it will start slave threads for the good channels if skip-slave-start
     is disabled. Also as part of this fix, we have restructured
     create_slave_info_objects function to increase the code readability
     START SLAVE and STOP SLAVE, which are supposed to operate on all the
     channels, are also modified such that they will continue
     executing on all good channels even if they find one bad channel
     in between.