Initial implementation of HostEpoch

When host time is set, the diff between the BmcTime and the value is
saved to persistent storage;
When host time is retrieved, return the BmcTime plus the diff as
host's time.

Add the unit test cases for HostEpoch.

Change-Id: Ia55b93bfcba4f226ceaed8491136ea7afda7bd77
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/configure.ac b/configure.ac
index 03f8347..7a2ee4e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -64,6 +64,10 @@
 AS_IF([test "x$OBJPATH_HOST" == "x"], [OBJPATH_HOST="/xyz/openbmc_project/time/host"])
 AC_DEFINE_UNQUOTED([OBJPATH_HOST], ["$OBJPATH_HOST"], [The host epoch Dbus root])
 
+AC_ARG_VAR(HOST_OFFSET_FILE, [The file to save host time offset])
+AS_IF([test "x$HOST_OFFSET_FILE" == "x"], [HOST_OFFSET_FILE="/var/lib/obmc/saved_host_offset"])
+AC_DEFINE_UNQUOTED([HOST_OFFSET_FILE], ["$HOST_OFFSET_FILE"], [The file to save host time offset])
+
 
 AC_CONFIG_FILES([Makefile test/Makefile])
 AC_OUTPUT