Removed the duplicated entries for metrics.
the innodb.buffer_pool_pages_flushed has two different types in the two lines. Left it at unit64 based on the requirement from Cloud Database team.
fixed how the attributes are being pulled based on MySQL document:

* Relay_Log_Size should be max_relay_log_size in system variable: http://dev.mysql.com/doc/refman/5.5/en/server-system-variables.html#sysvar_max_relay_log_size
* Slave_open_temp_tables should be in global variables: http://dev.mysql.com/doc/refman/5.5/en/server-status-variables.html#statvar_Slave_open_temp_tables
* Slave_retried_transactions should be in global variables: http://dev.mysql.com/doc/refman/5.5/en/server-status-variables.html#statvar_Slave_retried_transactions
Merge pull request #565 from wolfdancer/master

Removed the duplicated entries for metrics, fixed how attributes are being pulled