#219 Database.get_services return is insufficient

[Tiago Coutinho]

I am starting to use the services feature in Tango.

the Database.get_services(<service name>, <service instance>) method accepts a wildcard in the second parameter. However the result is a list of devices. With this information I cannot associate a device that implements the service with the service instance.

I believe nobody is using this feature yet. Having this into account I propose this method returns a list of strings in which the elements are alternatively <service instance> and <device name>
(this is similar what db.get_device_class_list does for classes and devices)

This way if a device is deleted without unregistering the service it is providing, it is still possible to later do a cleanup of the existing services.

Cheers