[Perf] Update references to telemetry.core.discover

tools/perf/core/perf_data_generator.py

 #!/usr/bin/env python
 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # pylint: disable=too-many-lines
 
 """Script to generate chromium.perf.json and chromium.perf.fyi.json in
 the src/testing/buildbot directory and benchmark.csv in the src/tools/perf
 directory. Maintaining these files by hand is too unwieldy.
 """
 import argparse
 import collections
 import csv
 import json
 import os
 import re
 import sys
 import sets
 
 
 from core import path_util
 path_util.AddTelemetryToPath()
 
 from telemetry import benchmark as benchmark_module
-from telemetry.core import discover
 from telemetry import decorators
 
+from py_utils import discover
+
 from core.sharding_map_generator import load_benchmark_sharding_map
 
 
 def add_builder(waterfall, name, additional_compile_targets=None):
   waterfall['builders'][name] = added = {}
   if additional_compile_targets:
     added['additional_compile_targets'] = additional_compile_targets
 
   return waterfall
 
@@ skipping 1041 matching lines @@
       return 0
     else:
       print ('The perf JSON config files are not up-to-date. Please run %s '
              'without --validate-only flag to update the perf JSON '
              'configs and benchmark.csv.') % sys.argv[0]
       return 1
   else:
     update_all_tests([fyi_waterfall, waterfall])
     update_benchmark_csv()
   return 0