test: Add test for GetVersions()

Also split and rename the cases in utest.cpp into test_signature and
test_version.

Tested: Verify test is built and passed.

Change-Id: Ibe59355936d9366be8e3f56760bff7384a28a28c
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/test/Makefile.am b/test/Makefile.am
index e0a13f5..da477d2 100755
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -40,7 +40,8 @@
 	../ubi/watch.cpp \
 	../static/item_updater_static.cpp \
 	../static/activation_static.cpp \
-	utest.cpp \
+	test_signature.cpp \
+	test_version.cpp \
 	msl_verify.cpp
 
 utest_LDADD = -lstdc++fs