An error is logged when loading a YAML configuration with 'type' instead of 'class'

In YamlConfiguration::parseControllerServices we try to first find `class` and fall back to `type` if it does not exist, but we log a scary error during the process, which might confuse users, since despite it, we are able to successfully parse the configuration:

`[2019-10-04 16:23:48.093] [org::apache::nifi::minifi::core::YamlConfiguration] [error] Unable to parse configuration file for component named 'SSLContextService' as required field 'class' is missing [in 'Controller Services' section of configuration file]`