Change the timestamp value to use the monotonic timer

Change the timestamp value to use the monotonic timer

- Problem: real-time timestamp causes various problems.
- Cause: If the time zone is changed or the system time is initialized,
  the wrong timestamp may be generated.
- Solution:
  1. Change to use the monotonic timer when creating a timestamp.
  2. Add new plugin API that enables the BLE plugin can save real-time
  timestamp.

Change-Id: I2508ecdb15977f6278fb2eeec89dc5caba77537f
Signed-off-by: saerome.kim <saerome.kim@samsung.com>