test/py: Handle a failure during configuration

If the build does not exist we can get an error when starting up:

  INTERNALERROR> Exception: .config does not exist; try passing --build
    option?
  Exception ignored in atexit callback: <function cleanup at ...>
  Traceback (most recent call last):
    File "test/py/conftest.py", line 697, in cleanup
    show_timings()
  File "test/py/conftest.py", line 644, in show_timings
    if ubconfig and ubconfig.timing:
                    ^^^^^^^^^^^^^^^
Fix this by setting up the timing member at the start.

Signed-off-by: Simon Glass <simon.glass@canonical.com>

test/py/conftest.py

@@ -301,6 +301,7 @@ def pytest_configure(config):
     ubconfig = ArbitraryAttributeContainer()
     ubconfig.brd = dict()
     ubconfig.env = dict()
+    ubconfig.timing = None
     not_found = []
 
     with log.section('Loading lab modules', 'load_modules'):