qa: Improve assert_start_raises_init_error output

Re-raising within the except-block would trigger excessive "During handling of the above exception, another exception occurred"-output.

Also changed comment - exceptions are raised in Python, not thrown.

test/functional/test_framework/test_node.py

@@ -712,11 +712,12 @@ class TestNode():
         extra_args: extra arguments to pass through to bitcoind
         expected_msg: regex that stderr should match when bitcoind fails
 
-        Will throw if bitcoind starts without an error.
+        Will raise if bitcoind starts without an error.
-        Will throw if an expected_msg is provided and it does not match bitcoind's stdout."""
+        Will raise if an expected_msg is provided and it does not match bitcoind's stdout."""
         assert not self.running
         with tempfile.NamedTemporaryFile(dir=self.stderr_dir, delete=False) as log_stderr, \
              tempfile.NamedTemporaryFile(dir=self.stdout_dir, delete=False) as log_stdout:
+            assert_msg = None
             try:
                 self.start(extra_args, stdout=log_stdout, stderr=log_stderr, *args, **kwargs)
                 ret = self.process.wait(timeout=self.rpc_timeout)
@@ -740,7 +741,7 @@ class TestNode():
                         if expected_msg != stderr:
                             self._raise_assertion_error(
                                 'Expected message "{}" does not fully match stderr:\n"{}"'.format(expected_msg, stderr))
-            except subprocess.TimeoutExpired:
+            except subprocess.TimeoutExpired as e:
                 self.process.kill()
                 self.running = False
                 self.process = None
@@ -749,6 +750,10 @@ class TestNode():
                     assert_msg += "with an error"
                 else:
                     assert_msg += "with expected error " + expected_msg
+                assert_msg += f" (cmd: {e.cmd})"
+
+            # Raise assertion outside of except-block above in order for it not to be treated as a knock-on exception.
+            if assert_msg:
                 self._raise_assertion_error(assert_msg)
 
     def add_p2p_connection(self, p2p_conn, *, wait_for_verack=True, send_version=True, supports_v2_p2p=None, wait_for_v2_handshake=True, expect_success=True, **kwargs):