PT-2268 - pt-online-schema-change 3.5.5 breaks on mysql5.7 with server_id 0

- Better check if server_id is defined
- Added test case

t/pt-online-schema-change/pt-2268.t

@@ -0,0 +1,72 @@
+#!/usr/bin/env perl
+
+BEGIN {
+    die "The PERCONA_TOOLKIT_BRANCH environment variable is not set.\n"
+    unless $ENV{PERCONA_TOOLKIT_BRANCH} && -d $ENV{PERCONA_TOOLKIT_BRANCH};
+    unshift @INC, "$ENV{PERCONA_TOOLKIT_BRANCH}/lib";
+};
+
+use strict;
+use warnings FATAL => 'all';
+
+use English qw(-no_match_vars);
+use Test::More;
+
+use PerconaTest;
+use Sandbox;
+
+require "$trunk/bin/pt-online-schema-change";
+
+my $dp = new DSNParser(opts=>$dsn_opts);
+my $sb = new Sandbox(basedir => '/tmp', DSNParser => $dp);
+
+my $dbh = $sb->get_dbh_for('master');
+my $slave_dbh = $sb->get_dbh_for('slave1');
+my $dsn = $sb->dsn_for("master");
+
+if ( !$dbh ) {
+   plan skip_all => 'Cannot connect to sandbox master';
+}
+elsif ( !$slave_dbh ) {
+   plan skip_all => 'Cannot connect to sandbox slave';
+}
+else {
+   plan tests => 2;
+}
+
+# The sandbox servers run with lock_wait_timeout=3 and it's not dynamic
+# so we need to specify --set-vars innodb_lock_wait_timeout=3 else the
+# tool will die.
+my @args = (qw(--set-vars innodb_lock_wait_timeout=3));
+my $output;
+my $exit_status;
+
+$sb->load_file('master', "t/pt-online-schema-change/samples/pt-2048.sql");
+
+my $orig_id;
+my $sql = 'SELECT @@server_id';
+($orig_id) = $dbh->selectrow_array($sql);
+$dbh->do('SET GLOBAL server_id=0');
+
+($output, $exit_status) = full_output(
+    sub { pt_online_schema_change::main(@args, "$dsn,D=test,t=joinit",
+            '--execute', '--charset=utf8', '--chunk-size', '2', '--alter', 'engine=innodb',
+        ),
+    },
+    stderr => 1,
+);
+
+is(
+   $exit_status,
+   0,
+   'pt-osc works with server_id=0'
+);
+
+$dbh->do("SET GLOBAL server_id=${orig_id}");
+
+# #############################################################################
+# Done.
+# #############################################################################
+$sb->wipe_clean($dbh);
+ok($sb->ok(), "Sandbox servers") or BAIL_OUT(__FILE__ . " broke the sandbox");
+done_testing;