Forking from T365123#9904990:
In https://gerrit.wikimedia.org/r/992104, the default log level for YAML loading errors was increased from debug to error to address T355256.
However, given the way conftool enumerates possibly-non-existent config files during initialization, and this is now rather noisy. We should either (1) not attempt to config load files that do not exist or (2) limit the scope of ERROR logging to only the invalid-YAML case (original intent).