zdtm/fork: print children wait status

05:57:35.640:  1238: FAIL: fork.c:80: Task 16275 didn't exit (errno = 10 (No child processes))

There is no info about the killing signal in logs, add it.

https://jira.sw.ru/browse/PSBM-87579Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

test/zdtm/transition/fork.c

@@ -77,12 +77,12 @@ int main(int argc, char **argv)
 				break;
 
 			if (!WIFEXITED(status)) {
-				fail("Task %d didn't exit", wpid);
+				fail("Task %d didn't exit with status %d", wpid, status);
 				goto out;
 			}
 
 			if (WEXITSTATUS(status) != 0) {
-				fail("Task %d exited with wrong code", wpid);
+				fail("Task %d exited with wrong status %d", wpid, status);
 				goto out;
 			}
 		}