Abstract value_string as common utility

Originally, we use this in scsi-lowlevel.c only, this works as static
function. It also could be used to dump ISCSI opcode, so move it into
common utils.h/utils.c.

Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>

lib/Makefile.am

@@ -6,7 +6,7 @@ libiscsipriv_la_SOURCES = \
 	connect.c crc32c.c discovery.c init.c \
 	login.c nop.c pdu.c iscsi-command.c \
 	scsi-lowlevel.c socket.c sync.c task_mgmt.c \
-	logging.c
+	logging.c utils.c
 
 if TARGET_OS_IS_WIN32
 libiscsipriv_la_SOURCES += ../win32/win32_compat.c