bdd: __tracbackhide__ in QuteProcess._wait_for_*

This should improve the output we got here:
https://ci.appveyor.com/project/The-Compiler/qutebrowser/build/master-2404/job/gr7m54km6h6nul04

tests/integration/testprocess.py

@@ -338,6 +338,7 @@ class Process(QObject):
 
         Return: either the found line or None.
         """
+        __tracebackhide__ = True
         for line in self._data:
             matches = []
 
@@ -358,6 +359,7 @@ class Process(QObject):
 
         Called via wait_for.
         """
+        __tracebackhide__ = True
         message = kwargs.get('message', None)
         if message is not None:
             elided = quteutils.elide(repr(message), 50)