Move files common for mysql and mariadb under mysql-common

Because galera library path has to be set in mysql config file,
we create a symlink during install time to make sure that there is
always same path for mysql and mariadb and for all architectures.

Change-Id: Iea3264932ec621d3d7618c5c50cbe47a956fb332
Merge "Move files common for mysql and mariadb under mysql-common"