test: Fix up-self-test crash during out-of-tree builds

When the layout of the build tree doesn't match the expectations in
up-self-test, the test would crash failing to find UPower.conf. Pass the
path as a macro during build so we always know where it is.

src/Makefile.am

@@ -15,6 +15,7 @@ AM_CPPFLAGS = \
 	$(PIE_CFLAGS)						\
 	-I$(top_builddir)/src -I$(top_srcdir)/src		\
 	-I$(top_builddir)/ -I$(top_srcdir)/			\
+	-DUPOWER_CONF_PATH=\""$(top_srcdir)/etc/UPower.conf"\"	\
 	-DPACKAGE_LIBEXEC_DIR=\""$(libexecdir)"\"		\
 	-DPACKAGE_SYSCONF_DIR=\""$(sysconfdir)"\"		\
 	-DPACKAGE_DATA_DIR=\""$(datadir)"\"			\

src/up-self-test.c

@@ -295,11 +295,7 @@ main (int argc, char **argv)
 #endif
 	g_test_init (&argc, &argv, NULL);
 
-	/* make check, vs. make distcheck */
-	if (g_file_test ("../etc/UPower.conf", G_FILE_TEST_EXISTS))
-		g_setenv ("UPOWER_CONF_FILE_NAME", "../etc/UPower.conf", TRUE);
-	else
-		g_setenv ("UPOWER_CONF_FILE_NAME", "../../../etc/UPower.conf", TRUE);
+	g_setenv ("UPOWER_CONF_FILE_NAME", UPOWER_CONF_PATH, TRUE);
 
 	/* tests go here */
 	g_test_add_func ("/power/backend", up_test_backend_func);