Add implementation of a system file interface

Implement simple read/write file operation semantics for the commit
operation. Add unit tests using the mock sys interface to verify the
behaviors.

Signed-off-by: Kun Yi <kunyi@google.com>
Change-Id: I75f8005561ab342138375bccb46c21e2841aa5e1
diff --git a/test/Makefile.am b/test/Makefile.am
index 9f41737..b2fa580 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -11,11 +11,15 @@
 
 # Run all 'check' test programs
 check_PROGRAMS = \
+	sys_file_unittest \
 	handler_open_unittest \
 	handler_readwrite_unittest \
 	handler_unittest
 TESTS = $(check_PROGRAMS)
 
+sys_file_unittest_SOURCES = sys_file_unittest.cpp
+sys_file_unittest_LDADD = $(top_builddir)/sys_file.o
+
 handler_unittest_SOURCES = handler_unittest.cpp
 handler_unittest_LDADD = $(PHOSPHOR_LOGGING_LIBS) \
 	$(top_builddir)/handler.o \