Add support for check_address as default in database CheckCommand objects

Add support for check_address as default in database CheckCommand objects

1. set the default hostname to the "$check_address$" for multiple CheckCommands
2. add support for  "$check_address$" for ping4 and ping6 commands which don't import the ipv4-or-ipv6 template

This commit changes the default address for redis, mongodb and elasticsearch to
use check_address instead of localhost. Users who might not have set this explicitly
in their services should adopt this.

Signed-off-by: Michael Friedrich <michael.friedrich@icinga.com>
Signed-off-by: Gunnar Beutner <gunnar.beutner@icinga.com>