Code review comment for lp:~gryp/percona-toolkit/ptosc-lagwaiter-ptheartbeat

This will make a good addition to the tool. Thanks for testing it. Before we merge, let's make the following changes:

1. Rename plugin hook to get-slave-lag

2. Rewrite code like:

my $get_lag;
if ( $plugin && $plugin->can('get-slave-lag') ) {
    $get_lag = $plugin->override_slavelag_check(oktorun => \$oktorun);
}
else {
    $get_lag = sub {...}
}

3. Break the code comments "# The plugin is able"... on/before 80 cols.