Fix the problem that can't add a device to a user

Fix the problem that can't add a device to a user

- Problem: Once user_id exceeded 0xFFFF then can't add a device to the
  user anymore.
- Cause: ua-manager is managing user_id as a maximun 16-bit unsigned
  integer.
- Solution: change user_id type to 32-bit integer.

Change-Id: I31cdf1fe7bc7ed580091f81fd50f48882f715cbe
Signed-off-by: saerome.kim <saerome.kim@samsung.com>