Implement part of BmcEpoch

Add BmcEpoch which inherits EpochBase and will handle times for BMC,
it is partly implemented.

Add unit test cases to test basic functions.

Change-Id: Ia5e4d0f884156d238f3f84df490a2efbce43e89a
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/Makefile.am b/Makefile.am
index 4b4cf02..3eef41a 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -5,7 +5,8 @@
 noinst_LTLIBRARIES = libtimemanager.la
 
 libtimemanager_la_SOURCES = \
-	epoch_base.cpp
+	epoch_base.cpp \
+	bmc_epoch.cpp
 
 phosphor_timemanager_SOURCES = \
 	main.cpp