Don't use fork to start the notebook in js tests

It can encounter a weird segfault on OS X with sqlite when Qt is present (?!)

The main reason to use the fork was to get the port number,
but this is easy now that notebooks write a server-info file.

Further advantage is that the symptom of a failed server start
is no longer silence and hanging tests, but an actual failure with the server's log output.

IPython/testing/iptestcontroller.py

@@ -19,8 +19,8 b' test suite.'
 from __future__ import print_function
 
 import argparse
+import json
 import multiprocessing.pool
-from multiprocessing import Process, Queue
 import os
 import shutil
 import signal
@@ -28,7 +28,7 b' import sys'
 import subprocess
 import time
 
-from .iptest import have, test_group_names as py_test_group_names, test_sections
+from .iptest import have, test_group_names as py_test_group_names, test_sections, StreamCapturer
 from IPython.utils.path import compress_user
 from IPython.utils.py3compat import bytes_to_str
 from IPython.utils.sysinfo import get_sys_info
@@ -211,8 +211,10 b' class JSController(TestController):'
         os.makedirs(os.path.join(self.nbdir.name, os.path.join(u'sub ∂ir2', u'sub ∂ir 1b')))
         
         # start the ipython notebook, so we get the port number
+        self.server_port = 0
         self._init_server()
-        self.cmd.append('--port=%s' % self.server_port)
+        if self.server_port:
+            self.cmd.append("--port=%i" % self.server_port)
 
     def print_extra_info(self):
         print("Running tests with notebook directory %r" % self.nbdir.name)
@@ -223,36 +225,60 b' class JSController(TestController):'
 
     def _init_server(self):
         "Start the notebook server in a separate process"
-        self.queue = q = Queue()
-        self.server = Process(target=run_webapp, args=(q, self.ipydir.name, self.nbdir.name))
-        self.server.start()
-        self.server_port = q.get()
+        self.server_command = command = [sys.executable,
+            '-m', 'IPython.html',
+            '--no-browser',
+            '--ipython-dir', self.ipydir.name,
+            '--notebook-dir', self.nbdir.name,
+        ]
+        # ipc doesn't work on Windows, and darwin has crazy-long temp paths,
+        # which run afoul of ipc's maximum path length.
+        if sys.platform.startswith('linux'):
+            command.append('--KernelManager.transport=ipc')
+        self.stream_capturer = c = StreamCapturer()
+        c.start()
+        self.server = subprocess.Popen(command, stdout=c.writefd, stderr=subprocess.STDOUT)
+        self.server_info_file = os.path.join(self.ipydir.name,
+            'profile_default', 'security', 'nbserver-%i.json' % self.server.pid
+        )
+        self._wait_for_server()
+    
+    def _wait_for_server(self):
+        """Wait 30 seconds for the notebook server to start"""
+        for i in range(300):
+            if self.server.poll() is not None:
+                return self._failed_to_start()
+            if os.path.exists(self.server_info_file):
+                self._load_server_info()
+                return
+            time.sleep(0.1)
+        print("Notebook server-info file never arrived: %s" % self.server_info_file,
+            file=sys.stderr
+        )
+    
+    def _failed_to_start(self):
+        """Notebook server exited prematurely"""
+        captured = self.stream_capturer.get_buffer().decode('utf-8', 'replace')
+        print("Notebook failed to start: ", file=sys.stderr)
+        print(self.server_command)
+        print(captured, file=sys.stderr)
+    
+    def _load_server_info(self):
+        """Notebook server started, load connection info from JSON"""
+        with open(self.server_info_file) as f:
+            info = json.load(f)
+        self.server_port = info['port']
 
     def cleanup(self):
+        self.stream_capturer.halt()
+        try:
         self.server.terminate()
-        self.server.join()
+        except OSError:
+            # already dead
+            pass
+        self.server.wait()
         TestController.cleanup(self)
 
-def run_webapp(q, ipydir, nbdir, loglevel=0):
-    """start the IPython Notebook, and pass port back to the queue"""
-    import os
-    import IPython.html.notebookapp as nbapp
-    import sys
-    sys.stderr = open(os.devnull, 'w')
-    server = nbapp.NotebookApp()
-    args = ['--no-browser']
-    args.extend(['--ipython-dir', ipydir,
-                 '--notebook-dir', nbdir,
-                 '--log-level', str(loglevel),
-    ])
-    # ipc doesn't work on Windows, and darwin has crazy-long temp paths,
-    # which run afoul of ipc's maximum path length.
-    if sys.platform.startswith('linux'):
-        args.append('--KernelManager.transport=ipc')
-    server.initialize(args)
-    # communicate the port number to the parent process
-    q.put(server.port)
-    server.start()
 
 def prepare_controllers(options):
     """Returns two lists of TestController instances, those to run, and those