alsa.lua: fix device name deduplication when reservation is enabled
This MR fixes the device name deduplication when reservation is enabled.
The audio devices are not created right away when the device reservation plugin is loaded, instead, they are created later when the plugin acquires the device name. This is a problem when deduplicating device names because the device is not stored as managed object yet. To fix this issue, we also check if the device name is added in the reservation. We consider a unique device name when the device name cannot be found in both the stored managed objects and plugin's device reservation object.
Fixes #241 (closed)