Add support for catalogs to Federatedx

The servers table table is already stored per catalog.

• Test that "servers" table works per catalog.
• Ensure that we create the 'servers' table in each catalog mysql's datadir.
• Ensure one can connect to from a server compiled with and without catalogs:
  (Same requirement as with catalogs and the connect engine)
• A table in another catalog.
• A table in a non catalog server.
• Add 'catalog' name to mysql.servers
• Remember to fix this in mysql_fix_privileges

Things to look at:
sql_servers.cc
bool servers_init(bool dont_read_servers_table)