Updated service.py and its dependencies

Updated service.py and its dependencies

This is to avoid service module dependency on importutils that are now
moved to oslo.utils.

The following changes are included:

 * neutron/openstack/common/eventlet_backdoor.py
  5d40e14 Remove code that moved to oslo.i18n
  90ae24b Remove redundant default=None for config options
  fcf517d Update oslo log messages with translation domains

 * neutron/openstack/common/loopingcall.py
  5d40e14 Remove code that moved to oslo.i18n
  e377393 Changes calcuation of variable delay
  ab5d5f1 Use timestamp in loopingcall
  bc48099 Log the function name of looping call
  fb4e863 Remove deprecated LoopingCall
  fcf517d Update oslo log messages with translation domains

 * neutron/openstack/common/service.py
  5d40e14 Remove code that moved to oslo.i18n
  6ede600 rpc, notifier: remove deprecated modules

 * neutron/openstack/common/systemd.py
  17c4e21 Fix docstring indentation in systemd

 * neutron/openstack/common/threadgroup.py
  5a1a016 Make stop_timers() method public
  fdc8883 Add graceful stop function to ThreadGroup.stop
  2d06d6c Simple typo correction
  4d18b57 threadgroup: use threading rather than greenthread

Change-Id: I4887545f861a93223e2c7cbcdd39efe991bff547