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/src/interfaces/clock.hpp b/src/interfaces/clock.hpp
index 0c355b7..b37ff3a 100644
--- a/src/interfaces/clock.hpp
+++ b/src/interfaces/clock.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include "types/duration_types.hpp"
+
 #include <chrono>
 
 namespace interfaces
@@ -8,15 +10,10 @@
 class Clock
 {
   public:
-    using duration = std::chrono::steady_clock::time_point::duration;
-    using rep = std::chrono::steady_clock::time_point::rep;
-    using period = std::chrono::steady_clock::time_point::period;
-    using time_point = std::chrono::steady_clock::time_point;
-
     virtual ~Clock() = default;
 
-    virtual time_point now() const noexcept = 0;
-    virtual uint64_t timestamp() const noexcept = 0;
+    virtual Milliseconds steadyTimestamp() const noexcept = 0;
+    virtual Milliseconds systemTimestamp() const noexcept = 0;
 };
 
 } // namespace interfaces