Stop scan on sensor when no monitoring application

Stop scan on sensor when no monitoring application

Issue: Presence/absence scanning on BLE/wifi plugin was not able to
stop in case only presence or only absence was started by application.

Reason: Even if only presence or only absence is started by application
ua-manager simultaneoulsy starts both presence and absence to keep their
detection cycle in sync.

Solution: Stop both presence and absence detection when stop detection
is called, if no application is monitioring on this sensor.

Change-Id: I1e54bad283932dfe3128628e98369a0070f9e623
Signed-off-by: Abhay Agarwal <ay.agarwal@samsung.com>