Merge bitcoin/bitcoin#32509: qa: feature_framework_startup_failures.py fixes & improvements (#30660 follow-up)

bf950c4544 qa: Improve suppressed errors output (Hodlinator)
075352ec8e qa: assert_raises_message() - search in str(e) (Hodlinator)
bd8ebbc4ab qa: Make --timeout-factor=0 result in a smaller factor (Hodlinator)
d8f05e7bf3 qa: Fix dormant bug caused by multiple --tmpdir (Hodlinator)

Pull request description:

  * Handle multiple `--tmpdir` args properly.
  * Handle `--timeout-factor=0` properly (fixes #32506).
  * Improve readability of expected error message (`assert_raises_message()`).
  * Make suppressed error output less confusing (`wait_for_rpc_connection()`).

ACKs for top commit:
  i-am-yuvi:
    re-ACK bf950c4544
  ismaelsadeeq:
    Code review and tested ACK bf950c45
  achow101:
    ACK bf950c4544
  janb84:
    LGTM ACK bf950c4544

Tree-SHA512: 8993f53e962231adef9cad92594dc6a8b8e979b1571d1381cd0fffa1929833b2163c68c03b6a6e29995006a3c3121822ec25ac7725e71ccdab8876ac24aae86c

test/functional/test_framework/util.py

@@ -102,9 +102,9 @@ def assert_raises_message(exc, message, fun, *args, **kwds):
     except JSONRPCException:
         raise AssertionError("Use assert_raises_rpc_error() to test RPC failures")
     except exc as e:
-        if message is not None and message not in repr(e):
+        if message is not None and message not in str(e):
             raise AssertionError("Expected substring not found in exception:\n"
-                                 f"substring: '{message}'\nexception: {repr(e)}.")
+                                 f"substring: '{message}'\nexception: {e!r}.")
     except Exception as e:
         raise AssertionError("Unexpected exception raised: " + type(e).__name__)
     else: