[lldb] [test] Rename '.categories' to 'categories'

[mgorny]

Summary

Make category-specifying files visible. There is really no good reason
to keep them hidden, and having them visible increases the chances
that someone will actually spot them.

[emaste]

No objection from me but I haven't been sufficiently involved in lldb's tests to approve.

[teemperor]

LGTM.

lldb/packages/Python/lldbsuite/test/test_result.py

def _getTestPath(self, test):
             return test.test_filename
         else:
             import inspect
             return inspect.getsourcefile(test.__class__)
 
     def _getFileBasedCategories(self, test):
         """
         Returns the list of categories to which this test case belongs by
-        collecting values of ".categories" files. We start at the folder the test is in
+        collecting values of "categories" files. We start at the folder the test is in
         and traverse the hierarchy upwards until the test-suite root directory.
         """
         start_path = self._getTestPath(test)
 
         import os.path
         folder = os.path.dirname(start_path)
 
         from lldbsuite import lldb_test_root as test_root
         if test_root != os.path.commonprefix([folder, test_root]):
             raise Exception("The test file %s is outside the test root directory" % start_path)
 
         categories = set()
         while not os.path.samefile(folder, test_root):
-            categories_file_name = os.path.join(folder, ".categories")
+            categories_file_name = os.path.join(folder, "categories")
             if os.path.exists(categories_file_name):
                 categories_file = open(categories_file_name, 'r')
                 categories_str = categories_file.readline().strip()
                 categories_file.close()
                 categories.update(categories_str.split(','))
             folder = os.path.dirname(folder)
 
         return list(categories)