Update UID of instant reprepare client

Update UID of instant reprepare client

- Requirement:
In order to start engine quickly, one of the clients needs to reprepare
instantly.

- Contents:
To make one of the clients reprepare instantly, this patch adds new
logic into the engine library. Through this patch, the engine library
will update the UID of the clieant which needs to reprepare instantly.
This UID update will occur when the connection of the service is changed.

Change-Id: I465c4e3444fbd177feb3bdabdb20338bbab5daf1
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>