PT-1551 New wait for master method to pt-table-checksum

This is part of PT-1554. While I was testing pt-table-checksum
ignore_columns.t was failing and it was because the original method in
pt-table-checksum to wait for the slaves to catch up, wasn't enough.
I added a new method who calls MySQL's SELECT MASTER_POS_WAIT from the
MasterSlave package.

bin/pt-table-checksum

@@ -6238,9 +6238,9 @@ sub find_replication_differences {
    }
    my ($dbh, $repl_table) = @args{@required_args};
 
-    
    my $tries = $self->{'OptionParser'}->get('replicate-check-retries') || 1; 
    my $diffs;
+
    while ($tries--) {
       my $sql
          = "SELECT CONCAT(db, '.', tbl) AS `table`, "
@@ -11271,6 +11271,10 @@ sub main {
 
             # Wait for the last checksum of this table to replicate
             # to each slave.
+            # MySQL 8+ replication is slower than 5.7 and the old wait_for_last_checksum alone 
+            # was failing. The new wait_for_slaves checks that Read_Master_Log_Pos on slaves is 
+            # greather or equal Position in the master
+            wait_for_slaves(master_dbh => $args{Cxn}->dbh(), master_slave => $ms, slaves => $slaves);
             wait_for_last_checksum(
                tbl          => $tbl,
                repl_table   => $repl_table,
@@ -12337,6 +12341,20 @@ sub have_more_chunks {
    return 1; # more chunks
 }
 
+sub wait_for_slaves {
+   my (%args) = @_;
+   my @required_args = qw(master_dbh master_slave slaves);
+   foreach my $arg ( @required_args ) {
+       die "I need a $arg argument" unless $args{$arg};
+   }
+   my ($master_dbh, $ms, $slaves) = @args{@required_args};
+
+   my $master_status = $ms->get_master_status($master_dbh);
+   foreach my $slave ( @$slaves ) {
+       $ms->wait_for_master(master_status => $master_status, slave_dbh => $slave->dbh());
+   }
+}
+
 sub wait_for_last_checksum {
    my (%args) = @_;
    my @required_args = qw(tbl repl_table slaves max_chunk have_time OptionParser);

t/pt-table-checksum/ignore_columns.t

@@ -42,14 +42,14 @@ $sb->load_file('master', 't/pt-table-checksum/samples/issue_94.sql');
 $slave_dbh->do("update test.issue_94 set c=''");
 
 $output = output(
-   sub { pt_table_checksum::main(@args, qw(-d test -t issue_94)) },
+   sub { pt_table_checksum::main(@args, qw(-d test --ignore-databases mysql -t issue_94)) },
    trf => sub { return PerconaTest::count_checksum_results(@_, 'DIFFS') },
 );
 is(
    $output,
    "1",
    "Diff when column not ignored"
-);
+) or diag($output);
 
 $output = output(
    sub { pt_table_checksum::main(@args, qw(-d test -t issue_94),
@@ -60,7 +60,7 @@ is(
    $output,
    "0",
    "No diff when column ignored"
-);
+) or diag($output);
 
 $output = output(
    sub { pt_table_checksum::main(@args, qw(-d test -t issue_94),

t/pt-table-checksum/samples/issue_94.sql

@@ -1,3 +1,4 @@
+CREATE DATABASE IF NOT EXISTS test;
 USE test;
 DROP TABLE IF EXISTS `issue_94`;
 CREATE TABLE `issue_94` (