consistent i18n placeholders (flake8 H701, H702, H703)

- eliminates ambiguously defined keywords in i18n strings which may
  become incorrectly ordered in a corresponding translation.
- ensures formatting operations occur outside of i18n calls
- use bare multiline string concatenation instead of 'ab' + \n 'cd'
- eliminates an 'empty localization string' (passing a variable to i18n
  function)

Change-Id: I0d78b978cc730e5fb892b80dfacaaf6687cd80be
eliminate 'except:' (flake8 H201)

Change-Id: Ic53b43b96c490557352be212ac79a7e8a249c21a
one import per line (flake8 H301)

Change-Id: Idb93169a0b64861bff22d06304c020865dd0a0ab