Use time mode owner enums in dbus interface

Dbus interface defines time mode owners in xyz::openbmc_project::Time.
Use the enums from the interface instead of repo defined enums and use
the generated code to do convertions between strings and enums.

Update unit tests accordingly.

Change-Id: Ic304aa3b4137375d208bb1702e0f64df512fc5a0
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/epoch_base.hpp b/epoch_base.hpp
index fedaeb6..778a5cd 100644
--- a/epoch_base.hpp
+++ b/epoch_base.hpp
@@ -38,10 +38,10 @@
         sdbusplus::bus::bus& bus;
 
         /** @brief The current time mode */
-        Mode timeMode = Mode::MANUAL;
+        Mode timeMode = Mode::Manual;
 
         /** @brief The current time owner */
-        Owner timeOwner = Owner::BOTH;
+        Owner timeOwner = Owner::Both;
 
         /** @brief Set current time to system
          *