Tweak comment message formatting so that it doesn't outwit pylint

Also, this is marginally more efficient due
to removing unnecessary dict accesses.

Old:
    ret['comment'] = some_format_string
    ret['comment'] = ret['comment'].format(...)
New:
    ret['comment'] = some_format_string.format(...)
    # ...with some extra syntactic complications due to complying
    # with line length limits.
Merge pull request #14649 from hulu/str-format-tweak

Tweak comment message formatting so that it doesn't outwit pylint