generate.py: generate clar cache in binary directory

The source directory should usually not be touched when using
out-of-tree builds. But next to the previously fixed "clar.suite" file, we
are also writing the ".clarcache" into the project's source tree,
breaking the builds. Fix this by also honoring the output directory for
the ".clarcache" file.

tests/generate.py

@@ -158,7 +158,7 @@ class TestSuite(object):
         return modules
 
     def load_cache(self):
-        path = os.path.join(self.path, '.clarcache')
+        path = os.path.join(self.output, '.clarcache')
         cache = {}
 
         try:
@@ -171,7 +171,7 @@ class TestSuite(object):
         return cache
 
     def save_cache(self):
-        path = os.path.join(self.path, '.clarcache')
+        path = os.path.join(self.output, '.clarcache')
         with open(path, 'wb') as cache:
             pickle.dump(self.modules, cache)