Fix N402 for nova/api

Fix N402 errors (single line docstring should end in a period)
for nova/api, part of a larger attempt to stop ignoring our own
hacking.py tests.

Fix tests that look at docs in extensions

Change-Id: I89d89d1fcf37c4e7740c36375da4c751d1b621ed
Merge "Fix N402 for nova/api"