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/trigger_action_mock.hpp b/tests/src/mocks/trigger_action_mock.hpp
index 586ac21..65585d8 100644
--- a/tests/src/mocks/trigger_action_mock.hpp
+++ b/tests/src/mocks/trigger_action_mock.hpp
@@ -7,6 +7,6 @@
 class TriggerActionMock : public interfaces::TriggerAction
 {
   public:
-    MOCK_METHOD(void, commit, (const std::string&, uint64_t, double),
+    MOCK_METHOD(void, commit, (const std::string&, Milliseconds, double),
                 (override));
 };