Restart JupyterHub after each install

Restarting JupyterHub should be non-disruptive, and helps
make the config changes come true ASAP.

tljh/installer.py

@@ -73,4 +73,4 @@ conda.ensure_conda_packages(USER_ENV_PREFIX, [
 ])
 systemd.reload_daemon()
 systemd.start_service('configurable-http-proxy')
-systemd.start_service('jupyterhub')
+systemd.restart_service('jupyterhub')

tljh/systemd.py

@@ -46,3 +46,14 @@ def start_service(name):
         'start',
         name
     ], check=True)
+
+
+def restart_service(name):
+    """
+    Restart service with given name.
+    """
+    subprocess.run([
+        'systemctl',
+        'restart',
+        name
+    ], check=True)