test-pattern: substitute the HTTP log timestamp too

We add a pattern matching the infamous timestamp in http log. Now, we should be
able to have change appears in https log without having to re-glob the whole
thing over and over.

tests/common-pattern.py

@@ -32,4 +32,8 b' substitutions = ['
      # (replacement patterns)
      br'$USUAL_BUNDLE2_CAPS$'
     ),
+    # HTTP log dates
+    (br' - - \[\d\d/.../2\d\d\d \d\d:\d\d:\d\d] "GET',
+     br' - - [$LOGDATE$] "GET'
+    ),
 ]