test: Fix parallel build error on tests

The test was using LDADD to link the objects, this results in below
error when building with `make check -j`

    *** No rule to make target '../openpower_update_manager-activation.o', needed by 'utest'. Stop.

Because the test depends on the objects to be pre-build, but there is no
rule in test/Makefile.am to build t he objects.

This commit changes it to add sources instead of linking to objects, so
parallel build works fine.

Tested: run `make check -j` without error.

Change-Id: Ie7aaac49756fdd3b8941c1dec8f693ec66f659ab
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/test/Makefile.am b/test/Makefile.am
index 1a94d0d..b58ac66 100755
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -28,15 +28,18 @@
 	-lcrypto
 
 utest_SOURCES = \
+	../activation.cpp \
+	../version.cpp \
+	../item_updater.cpp \
+	../org/openbmc/Associations/server.cpp \
+	../image_verify.cpp \
+	../msl_verify.cpp \
+	../ubi/activation_ubi.cpp \
+	../ubi/item_updater_ubi.cpp \
+	../ubi/serialize.cpp \
+	../ubi/watch.cpp \
 	utest.cpp \
 	msl_verify.cpp
+
 utest_LDADD = \
-	$(top_builddir)/openpower_update_manager-activation.o \
-	$(top_builddir)/openpower_update_manager-version.o \
-	$(top_builddir)/ubi/openpower_update_manager-serialize.o \
-	$(top_builddir)/ubi/openpower_update_manager-watch.o \
-	$(top_builddir)/openpower_update_manager-item_updater.o \
-	$(top_builddir)/org/openbmc/Associations/openpower_update_manager-server.o \
-	$(top_builddir)/image_verify.cpp \
-	$(top_builddir)/msl_verify.cpp \
 	-lstdc++fs