refactor: improve docker digest lookup logging (#1119)

lib/manager/docker/package.js

@@ -24,6 +24,9 @@ async function getPackageUpdates(config) {
   if (currentDigest || config.pinDigests) {
     logger.debug('Checking docker pinDigests');
     const newDigest = await dockerApi.getDigest(depName, currentTag);
+    if (!newDigest) {
+      logger.debug({ content: config.content }, 'Dockerfile no digest');
+    }
     if (newDigest && config.currentDigest !== newDigest) {
       const upgrade = {};
       upgrade.newTag = currentTag || 'latest';

lib/manager/docker/registry.js

@@ -29,7 +29,7 @@ async function getDigest(name, tag = 'latest') {
     logger.debug({ digest }, 'Got docker digest');
     return digest;
   } catch (err) {
-    logger.warn({ err, name, tag }, 'Error getting docker image digest');
+    logger.info({ err, name, tag }, 'Error looking up docker image digest');
     return null;
   }
 }