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

Change-Id: Id0bb8f6b6091289275864bf4dd6a6890d11b4782

Change-Id: I2856f50977b1959801d66e7bc73fe54d24d43801

It comes as dependency from main wsrep packages and it differs
between versions of OS.

Change-Id: I2b50edaa19e52009766bca9fa31c566f59ff9319

Change-Id: I91f55d599f5291f34bfa81f55dafd6734606e1cc

This also installs 2 additional packages (libdbd-mysql and
python-pymysql) that are required for running the collectd plugins.