Sync harmless changes from oslo-incubator

Includes these commits:

  3948aee Highlighting the deprecated nature of 'log-format'.
  b21fc56 Fix bad default for show_deleted
  d28fa69 python3: Add python3 compatibility.
  0bf03b7 Add network_utils.urlsplit
  e456727 Remove useless logging in networks_utils
  7119e29 Enable hacking H404 test.
  b41862d Use param keyword for docstrings
  2f01388 Use Python 3.x compatible except construct
  e3545f8 Enable hacking H402 test
  484a1df Enable hacking H403 test
  35660da Enable hacking H401 test
  874249e Add support for requirements.txt.
  b135234 Remove the notifier and its dependencies from log.py
  926b3e9 Fixes import order nits

Changes which may look not look so harmless:

 - the common get_admin_context() method is not used by Nova
 - network_utils.urlsplit() is added but not used yet
 - suppport for requirements.txt is added to patch_tox_venv but
   actually it doesn't use those files

Change-Id: I03e67f4648dcaf57620f11e63cfd8e7dbe3665cb
Merge "Sync harmless changes from oslo-incubator"