Log translation hint for Heat.engine (part3)

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: Ib91983e6e61b4d6ddbbed0f95dc98cbde1d4f673
Merge "Log translation hint for Heat.engine (part3)"