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/test/Makefile.am b/test/Makefile.am
index 26c4c15..bdd258e 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -7,7 +7,8 @@
 
 test_SOURCES = \
     TestEpochBase.cpp \
-    TestBmcEpoch.cpp
+    TestBmcEpoch.cpp \
+    TestHostEpoch.cpp
 
 test_LDADD = $(top_builddir)/libtimemanager.la