add mysql_read_timeout and mysql_write_timeout

[azrle]

MHA can be hung when doing DBI->connect and reading from server if we don't have a mysql_read_timeout.

Here are procedures to reproduce the problem:

• Server
  We block 4th and following output packets from MySQL server.
  It simulate some cases when the server suddenly goes down.

sudo iptables -I OUTPUT -p tcp --destination $CLIENT_IP --source-port 3306 -m recent --rdest --name block-mysql --set

sudo iptables -A OUTPUT -p tcp --source-port 3306 -m recent --name block-mysql --rdest --rcheck --hitcount 3 -j DROP

sudo iptables -L -v
Chain INPUT (policy ACCEPT 1339 packets, 118K bytes)
 pkts bytes target     prot opt in     out     source               destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
Chain OUTPUT (policy ACCEPT 1167 packets, 92928 bytes)
 pkts bytes target     prot opt in     out     source               destination
   88  6708            tcp  --  any    any     anywhere             CLIENT_IP            tcp spt:mysql recent: SET name: block-mysql side: dest mask: 255.255.255.255
    0     0 DROP       tcp  --  any    any     anywhere             anywhere             tcp spt:mysql recent: CHECK hit_count: 3 name: block-mysql side: dest mask: 255.255.255.255

# clear counter
echo / | sudo tee /proc/net/xt_recent/block-mysql

cat /proc/net/xt_recent/block-mysql
# empty

• Client
  When you run the following client script, it will hang there. And after adding mysql_read_timeout, the problem will be solved.

use DBI;

my $SERVER = '10.0.0.2';
my $dbh = DBI->connect(
    "DBI:mysql:;host=$SERVER;"
      . "port=3306;mysql_connect_timeout=5"
      # . ";mysql_read_timeout=5"
    , 'root', 'rootpass',
    { PrintError => 0, RaiseError => 0 }
);
die "failed to connect: $DBI::errstr" unless $dbh;
print "OK\n";

Value $connect_timeout is used because it's shorter than $wait_timeout and we hope MHA can fail faster in this case.

cc: @hirose31