Bluetooth: Get the included service 128bit UUID

This adds reading of included service attribute 128bit UUID.
The limitation of this solution is that if several attr handle-range
pairs will be received, this will read first attribute UUID and then
start discovery from the the succeeding handle.

ZEP-373

Discovery related test results:

 2/76   GATT   TC_GAD_CL_BV_02_C   PASS
 3/76   GATT   TC_GAD_CL_BV_03_C   PASS
 4/76   GATT   TC_GAD_CL_BV_04_C   PASS
 5/76   GATT   TC_GAD_CL_BV_05_C   PASS
 6/76   GATT   TC_GAD_CL_BV_06_C   PASS

Change-Id: I27185b3a3ae96c9c03b0f356492df18ba83b183a
Signed-off-by: Mariusz Skamra <mariusz.skamra@tieto.com>