Add cluster CPU usage monitoring

[svaroqui]

If thread pool is enable

MariaDB [(none)]> show global status like 'thread%th%'; +-------------------------+-------+ | Variable_name | Value | +-------------------------+-------+ | Threadpool_idle_threads | 4 | | Threadpool_threads | 5 | +-------------------------+-------+

If and only if thread pool is enable computing thread Threadpool_threads-Threadpool_idle_threads should be store inside cluster stat object

an other way to compute CPU usage from SQL in MariaBD is to look at select SUM(CPU_TIME) FROM INFORMATION_SCHEMA.USER_STATISTICS\G when USER STATISICS is enable A force user statistic need to be implemented to share a cluster in the cloud for us to compute

One should explore MySQL alternative as MySQL thread pool is commercial usage only

[svaroqui]

We need to enable graphite for the thread pool metric when a cluster is shared for cloud usage thais will enable to trigger alert on cloud CPU usage exceeded to decide about scale up requirement and DBAAS action , by using graphite such metrics can be queries for average 75% and pick usage