invoke: correctly infer version for 0.1.0-vintage plugins

Older plugins return a known error when issued the VERSION command.
Capture this error and report it as a 0.1.0 version plugin.

libcni/api.go

@@ -67,8 +67,6 @@ func (c *CNIConfig) GetVersionInfo(pluginType string) (version.PluginInfo, error
 		return nil, err
 	}
 
-	// TODO: if error is because plugin is old and VERSION command is unrecognized
-	// then do the right thing and return version.PluginSupports("0.1.0"), nil
 	return invoke.ExecPluginForVersion(pluginPath)
 }