resilient: find doesn't fail if files have wrong permissions

we have webrunners where some files don't belong to correct user in partitions. In this case, find fails and we get this error:

Traceback (most recent call last):
  File "/opt/slapgrid/01ce71861bb9c5883cdbdf8af74c5d1f/bin/runner-exporter", line 83, in <module>
    sys.exit(slapos.resilient.runner_exporter.runExport())
  File "/opt/slapgrid/01ce71861bb9c5883cdbdf8af74c5d1f/eggs/slapos.toolbox-0.100-py2.7.egg/slapos/resilient/runner_exporter.py", line 182, in runExport
    modified_file_list = getBackupFilesModifiedDuringExportList(args, export_start_date)
  File "/opt/slapgrid/01ce71861bb9c5883cdbdf8af74c5d1f/eggs/slapos.toolbox-0.100-py2.7.egg/slapos/resilient/runner_exporter.py", line 106, in getBackupFilesModifiedDuringExportList
    'find', 'instance', '-cmin',  str(export_time / 60), '-type', 'f', '-path', '*/srv/backup/*'
  File "/opt/slapgrid/01ce71861bb9c5883cdbdf8af74c5d1f/parts/python2.7/lib/python2.7/subprocess.py", line 223, in check_output
    raise CalledProcessError(retcode, cmd, output=output)
subprocess.CalledProcessError: Command '('find', 'instance', '-cmin', '0.335502366225', '-type', 'f', '-path', '*/srv/backup/*')' returned non-zero exit status 1

Make find don't go into directories with wrong permissions