Fixed issue with wrong timestamp

Telemetry service used steady_clock for generating timestamps, but it
produced incorrect time. This change makes telemetry service use
steady_clock for intervals and system_clock for timestamps.

Changed readings timestamp to display current timestamp instead of a
time when reading was received.

Tested:
- correct timestamp is visible on dbus
- other telemetry service features are still working

Change-Id: Ic49f45640532cfffaeff5e0bd5591e6d99e5def5
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/tests/src/mocks/sensor_listener_mock.hpp b/tests/src/mocks/sensor_listener_mock.hpp
index 3a61519..a5c0331 100644
--- a/tests/src/mocks/sensor_listener_mock.hpp
+++ b/tests/src/mocks/sensor_listener_mock.hpp
@@ -18,10 +18,10 @@
             .WillByDefault(InvokeWithoutArgs([this] { sensorUpdated(); }));
     }
 
-    MOCK_METHOD(void, sensorUpdated, (interfaces::Sensor&, uint64_t),
+    MOCK_METHOD(void, sensorUpdated, (interfaces::Sensor&, Milliseconds),
                 (override));
-    MOCK_METHOD(void, sensorUpdated, (interfaces::Sensor&, uint64_t, double),
-                (override));
+    MOCK_METHOD(void, sensorUpdated,
+                (interfaces::Sensor&, Milliseconds, double), (override));
 
     MOCK_METHOD(void, sensorUpdated, (), ());
 };