Fixed flaky tests

The two tests previously tested assertions against the replica
after executing changes in the source without waiting for the
replication to converge.

t/pt-table-sync/char_chunking.t

@@ -37,13 +37,7 @@ $sb->create_dbs($master_dbh, ['test']);
 $sb->load_file('master', "t/lib/samples/char-chunking/ascii.sql", "test");
 $master_dbh->do('alter table test.ascii drop column `i`');
 
-wait_until(
-   sub {
-      my $row;
-      eval {$row = $slave_dbh->selectall_arrayref("select * from test.ascii");};
-      return 1 if $row && @$row > 100;
-   },
-);
+$sb->wait_for_slaves();
 
 $slave_dbh->do('delete from test.ascii where c like "Zesus%"');
 

t/pt-table-sync/pt-1256.t

@@ -74,6 +74,8 @@ like(
    "PT-1256 Set the correct charset"
 );
 
+$sb->wait_for_slaves();
+
 SKIP: {
    my $vp = VersionParser->new($master_dbh);
    if ($vp->cmp('8.0') > -1 && $vp->cmp('8.0.14') < 0 && $vp->flavor() !~ m/maria/i) {
@@ -91,6 +93,8 @@ SKIP: {
     $output = `$trunk/bin/pt-table-sync --execute --lock-and-rename h=127.1,P=12345,u=msandbox,p=msandbox,D=test,t=t1 t=t2 2>&1`;
     $output = `/tmp/12345/use -e 'show create table test.t2'`;
     like($output, qr/COMMENT='test1'/, '--lock-and-rename worked');
+
+    $sb->wait_for_slaves();
 
     #4
     $row = $slave1_dbh->selectrow_hashref("SELECT f2 FROM test.t2 WHERE id = 1");