Appended a command for mha4mysql-manager: masterha_paxos_lock

I appended a command for mha4mysql-manager: masterha_paxos_lock
Using this command to lock/unlock the majority of all nodes, can ensure that only one manager is running.

Usage:

Lock the majority of all nodes:
masterha_paxos_lock --conf=/etc/app1.cnf --holder=host1 --lock

Unlock the majority of all nodes:
masterha_paxos_lock --conf=/etc/app1.cnf --holder=host1 --unlock

I make it because I need run masterha_master_switch on all nodes. On each node, there is a mha4mysql-manager.
I name it as masterha_paxos_lock,because I use the majority(> 1/2) to confirm the result. It's similar to http://en.wikipedia.org/wiki/Paxos_(computer_science)

This update composed of the following file appends:
mha4mysql-manager/bin/masterha_paxos_lock  
mha4mysql-manager/lib/PaxosLock.pm  
mha4mysql-node/bin/try_paxos_lock(in repository mha4mysql-node)