fix deprecated sql_connection, idle_timeout

DEFAULT/sql_connection is replaced by database/connection
DEFAULT/sql_idle_timeout is replaced by database/idle_timeout

deprecated params are handled by warning like other modules

Change-Id: I1b8e61ac452b69fb611254562d1a42c2732c3c8e
require mysql binding for mysql db only

the requirement for the mysql module was introduces
with Change-Id: Ie0011102d9f4dfcd50f24afcb73072090c914011

If you do not use mysql (eg. because you prefer postgres),
the module is not usable without this patch.
The implementation is similar to puppet-keystone.

Change-Id: I42b7f75fe103d4e64d8991bcc9c8a20aef8f353d