Support reading VERSION_ID without quotes

The VERSION_ID value in /etc/os-release recently had its surrounding
quotation marks removed.  Update the code to be able to read values out
of /etc/os-release either with or without quotes, and make it a utility
function so that it can be used in multiple places.

Props to the phosphor-bmc-code-mgmt repo for the elegant implementation.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I348625ba49214ab2977d9e70a4337299bef5ed3a

Change-Id: I9d201954a8116dfda32d096a347e150d93fbfb46
diff --git a/Makefile.am b/Makefile.am
index 2c6aedc..0ef7221 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -57,7 +57,8 @@
 	elog_meta.cpp \
 	elog_serialize.cpp \
 	sdjournal.cpp \
-	extensions.cpp
+	extensions.cpp \
+	util.cpp
 
 # Be sure to build needed files before compiling
 BUILT_SOURCES = \