Test: fix shared random test checking bad errno

The test was checking for EISDIR which is a Linux-ism making other OSes
unhappy. Instead of checking for a negative specific errno value, just make
sure it's negative indicating an error. We don't need more for this test.

Signed-off-by: David Goulet <dgoulet@torproject.org>

src/test/test_shared_random.c

@@ -638,11 +638,7 @@ test_state_load_from_disk(void *arg)
 
   /* Try to load the directory itself. Should fail. */
   ret = disk_state_load_from_disk_impl(dir);
-#ifdef _WIN32
-  tt_int_op(ret, OP_EQ, -EACCES);
-#else
-  tt_int_op(ret, OP_EQ, -EISDIR);
-#endif
+  tt_int_op(ret, OP_LT, 0);
 
   /* State should be non-existent at this point. */
   the_sr_state = get_sr_state();