test: util: Introduce fail_args()

This macro is very similar to fail() but supports variable number of
arguments to print format strings.

Signed-off-by: Phil Sutter <psutter@redhat.com>

test/suites/api/util.h

@@ -29,6 +29,13 @@
         exit(1);                                                                         \
     } while (0)
 
+#define fail_args(msg, ...)                                      \
+    do {                                                         \
+        failhdr;                                                 \
+        fprintf(stderr, msg "\n", __VA_ARGS__);                  \
+        exit(1);                                                 \
+    } while(0)
+
 /* Assumes json_error_t error */
 #define check_errors(code_, texts_, num_, source_, line_, column_, position_)            \
     do {                                                                                 \