Merge bitcoin#19368: test: improve functional tests compatibility with BSD/macOS

3a7e794 test: retry when write to a socket fails on macOS (Ivan Metlushko)
8cf9d15 test: use pgrep for better compatibility (Ivan Metlushko)

Pull request description:

  Rationale: a few minor changes to make experience of running tests on macOS a bit better
  1.`pidof` is not available on BSD/macOS, while `pgrep` is present on BSD, Linux and macOS
  2. Add retry as a workaround for a weird behavior when writing to a socket (https://bugs.python.org/issue33450). Stacktrace attached

  Man pages:
  https://www.freebsd.org/cgi/man.cgi?query=pgrep&apropos=0&sektion=1&manpath=FreeBSD+6.0-RELEASE&arch=default&format=html
  https://man7.org/linux/man-pages/man1/pgrep.1.html

  Related to bitcoin#19281

  Stacktrace example:
  ```
  ...
  33/161 - feature_abortnode.py failed, Duration: 63 s

  stdout:
  2020-06-11T10:46:43.947000Z TestFramework (INFO): Initializing test directory /var/folders/2q/d5w9zh614r7g5c8r74ln3g400000gq/T/test_runner_₿_🏃_20200611_174102/feature_abortnode_128
  2020-06-11T10:46:45.199000Z TestFramework (INFO): Waiting for crash
  2020-06-11T10:47:15.921000Z TestFramework (INFO): Node crashed - now verifying restart fails
  2020-06-11T10:47:47.068000Z TestFramework (INFO): Stopping nodes
  [node 1] Cleaning up leftover process

  stderr:
  Traceback (most recent call last):
    File "/Users/xxx/Projects/bitcoin/test/functional/feature_abortnode.py", line 50, in <module>
      AbortNodeTest().main()
    File "/Users/xxx/Projects/bitcoin/test/functional/test_framework/test_framework.py", line 142, in main
      exit_code = self.shutdown()
    File "/Users/xxx/Projects/bitcoin/test/functional/test_framework/test_framework.py", line 266, in shutdown
      self.stop_nodes()
    File "/Users/xxx/Projects/bitcoin/test/functional/test_framework/test_framework.py", line 515, in stop_nodes
      node.stop_node(wait=wait)
    File "/Users/xxx/Projects/bitcoin/test/functional/test_framework/test_node.py", line 318, in stop_node
      self.stop(wait=wait)
    File "/Users/xxx/Projects/bitcoin/test/functional/test_framework/coverage.py", line 47, in __call__
      return_val = self.auth_service_proxy_instance.__call__(*args, **kwargs)
    File "/Users/xxx/Projects/bitcoin/test/functional/test_framework/authproxy.py", line 142, in __call__
      response, status = self._request('POST', self.__url.path, postdata.encode('utf-8'))
    File "/Users/xxx/Projects/bitcoin/test/functional/test_framework/authproxy.py", line 107, in _request
      self.__conn.request(method, path, postdata, headers)
    File "/Users/xxx/.pyenv/versions/3.5.6/lib/python3.5/http/client.py", line 1107, in request
      self._send_request(method, url, body, headers)
    File "/Users/xxx/.pyenv/versions/3.5.6/lib/python3.5/http/client.py", line 1152, in _send_request
      self.endheaders(body)
    File "/Users/xxx/.pyenv/versions/3.5.6/lib/python3.5/http/client.py", line 1103, in endheaders
      self._send_output(message_body)
    File "/Users/xxx/.pyenv/versions/3.5.6/lib/python3.5/http/client.py", line 936, in _send_output
      self.send(message_body)
    File "/Users/xxx/.pyenv/versions/3.5.6/lib/python3.5/http/client.py", line 908, in send
      self.sock.sendall(data)
  OSError: [Errno 41] Protocol wrong type for socket
  ```

ACKs for top commit:
  laanwj:
    ACK 3a7e794

Tree-SHA512: fefbe40ce94ab29f18bbbed2a434194b1384ffa5279b1d04db7a3708e3dd422bd9e450f1db3f95a1a851fac5a626ab533c6ebcfd7ede96f8ccae9e6f3e9fff92

Author: laanwj

test/functional/test_framework/authproxy.py

@@ -115,6 +115,8 @@ def _request(self, method, path, postdata):
         except OSError as e:
             retry = (
                 '[WinError 10053] An established connection was aborted by the software in your host machine' in str(e))
+            # Workaround for a bug on macOS. See https://bugs.python.org/issue33450
+            retry = retry or ('[Errno 41] Protocol wrong type for socket' in str(e))
             if retry:
                 self.__conn.close()
                 self.__conn.request(method, path, postdata, headers)

test/functional/test_runner.py

@@ -396,11 +396,12 @@ def run_tests(*, test_list, src_dir, build_dir, tmpdir, jobs=1, enable_coverage=
     args = args or []
 
     # Warn if bitcoind is already running
-    # pidof might fail or return an empty string if bitcoind is not running
     try:
-        if subprocess.check_output(["pidof", "bitcoind"]) not in [b'']:
+        # pgrep exits with code zero when one or more matching processes found
+        if subprocess.run(["pgrep", "-x", "bitcoind"], stdout=subprocess.DEVNULL).returncode == 0:
             print("%sWARNING!%s There is already a bitcoind process running on this system. Tests may fail unexpectedly due to resource contention!" % (BOLD[1], BOLD[0]))
-    except (OSError, subprocess.SubprocessError):
+    except OSError:
+        # pgrep not supported
         pass
 
     # Warn if there is a cache directory