Make max_connections and innodb_buffer_pool_size configurable
through soft params instead of hard.

Change-Id: Id0bb8f6b6091289275864bf4dd6a6890d11b4782

Usage:

  galera:
    master:
      innodb_buffer_pool_size: 1024M
    slave:
      innodb_buffer_pool_size: 1024M

If innodb_buffer_pool_size is not set then 35% of the available
ram will be allocated for the buffer pool.

Change-Id: Iaffa3f5b4ded8bc838f9d707916e360ed873c13b