add minio as a separate backend

Fixes #308

src/backups.js

@@ -89,6 +89,7 @@ function api(provider) {
         case 'caas': return caas;
         case 's3': return s3;
         case 'filesystem': return filesystem;
+        case 'minio': return s3;
         default: return null;
     }
 }

src/backuptask.js

@@ -26,6 +26,7 @@ function api(provider) {
         case 'caas': return caas;
         case 's3': return s3;
         case 'filesystem': return filesystem;
+        case 'minio': return s3;
         default: return null;
     }
 }

src/storage/s3.js

@@ -198,6 +198,7 @@ function testConfig(apiConfig, callback) {
     if (typeof apiConfig.bucket !== 'string') return callback(new BackupsError(BackupsError.BAD_FIELD, 'bucket must be a string'));
     if (typeof apiConfig.prefix !== 'string') return callback(new BackupsError(BackupsError.BAD_FIELD, 'prefix must be a string'));
     if ('signatureVersion' in apiConfig && typeof apiConfig.prefix !== 'string') return callback(new BackupsError(BackupsError.BAD_FIELD, 'signatureVersion must be a string'));
+    if ('endpoint' in apiConfig && typeof apiConfig.prefix !== 'string') return callback(new BackupsError(BackupsError.BAD_FIELD, 'endpoint must be a string'));
 
     // attempt to upload and delete a file with new credentials
     getBackupCredentials(apiConfig, function (error, credentials) {