Implement mode/owner and string conversions

Move Manager::convertToMode() to utils::strToMode();
Move Manager::convertToOwner() to utils::strToOwner();
Add utils::modeToStr() and utils::ownerToStr();
Adjust and add unit tests.

Change-Id: Ied35d0e732c477017e1b2db1a3464b0425b12387
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/Makefile.am b/Makefile.am
index 066dd33..57734d1 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -8,7 +8,8 @@
 	epoch_base.cpp \
 	bmc_epoch.cpp \
 	host_epoch.cpp \
-	manager.cpp
+	manager.cpp \
+	utils.cpp
 
 phosphor_timemanager_SOURCES = \
 	main.cpp