PT-1667 Added replication channels support to pt-archiver

bin/pt-archiver

@@ -6275,6 +6275,7 @@ sub main {
          OptionParser => $o,
          DSNParser    => $dp,
          Quoter       => $q,
+         channel      => $o->get('channel'),
       );
       # we get each slave's connection handler (and its id, for debug and reporting)
       for my $slave (@$lag_slaves_dsn) {
@@ -7472,6 +7473,18 @@ If C<LOAD DATA LOCAL INFILE> throws an error in the lines of C<The used
 command is not allowed with this MySQL version>, refer to the documentation
 for the C<L> DSN option.
 
+=item --channel
+
+type: string
+
+Channel name used when connected to a server using replication channels.
+Suppose you have two masters, master_a at port 12345, master_b at port 1236 and
+a slave connected to both masters using channels chan_master_a and chan_master_b.
+If you want to run pt-archiver to syncronize the slave against master_a, pt-archiver
+won't be able to determine what's the correct master since SHOW SLAVE STATUS
+will return 2 rows. In this case, you can use --channel=chan_master_a to specify
+the channel name to use in the SHOW SLAVE STATUS command.
+
 =item --charset
 
 short form: -A; type: string