[cygnus-common][MySQLBackend] Load Balance Connection Pooling

[pmo-sdr]

Implement MySQL Sink load Balancer exploiting new connection pooling capabilities #1598

The objetive of this new feature is to allow balanced sinks sharing the same connection pool.

Benefits:

• Reduced connection creation time among sinks.
• Centralized resource management
• Allows Cygnus to control max number of connections at database server level, even with several sinks running.
• Exploit database connection pooling capabilities.

es así entonces el pool no crecería de tamaño, quedando se en 1, a pesar de que pudiera tener un maximo mayor (con 5 ya me quedaba tranquilo), no? En cualquier caso anotaria otro FIXME comentando el porque y la idea futura. Originally posted by @AlvaroVega in https://github.com/telefonicaid/fiware-cygnus/pull/1600

[AlvaroVega]

I guess this load balancing feature is only used when a cygnus agent has several mysql sinks,