gdb.threads/manythreads.exp: can't read "test": no such variable

If interrupt_and_wait manages to trigger the FAIL path, we get:

  ERROR OCCURED: can't read "test": no such variable

gdb/testsuite/ChangeLog:
2015-04-01  Pedro Alves  <palves@redhat.com>

	* gdb.threads/manythreads.exp (interrupt_and_wait): Pass $message
	to fail instead of non-existent $test.

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2015-04-01  Pedro Alves  <palves@redhat.com>
+
+	* gdb.threads/manythreads.exp (interrupt_and_wait): Pass $message
+	to fail instead of non-existent $test.
+
 2015-04-01  Pedro Alves  <palves@redhat.com>
 
 	* lib/gdb.exp (gdb_spawn_with_cmdline_opts): Append space to

gdb/testsuite/gdb.threads/manythreads.exp

@@ -95,7 +95,7 @@ proc interrupt_and_wait { message } {
 	    #  foo () at foo.c:31
 	    #  31      bar ();
 	    #
-	    fail $test
+	    fail $message
 	}
     }
 }