Log translation hint for Heat.engine (part2)

Currently, Log translation is motivated by oslo's move to prioritized
translation of strings, as documented at
https://wiki.openstack.org/wiki/LoggingStandards#Log_Translation
- add log translation hints for warning, error and info levels
- move from LOG.warning to LOG.warn
- remove use of % as a string formatter, use the log functionality
  instead
Partial implements blueprint log-translation-hints

Change-Id: Ib943d41e7c1931af6d84e69ee3bc086221fc9725
Merge "Log translation hint for Heat.engine (part2)"