dock:: fix invalid dbus value.

some appid like 7kaa is invalid dbus value.

solution:
using 'd' + md5.encode(appid) as dbus value.

tower: https://tower.im/projects/1c0cd0c59ef941298c6e6b2ba6833b91/todos/2d6eb4c27fcc42c9a814a0f8084cab14/

Change-Id: I7f5fd95fd0e6c4ddaf59732e6e83eae816b7bf24