Prefer "message" attribute to match log resources

Chef 10.18 added message attribute to the log resource:
  http://tickets.opscode.com/browse/CHEF-3006

Fallback using the name attribute for older Chef versions.
Allow matching log statements with a Regexp

In addition to a String that has to match the whole log message, allow
matching with a Regexp (or any other object that returns true for
`object === <log message>`).