Report failed failable deliverables as errors

It does not abort the compose, but it's still an error. It should be
marked as such in the log. This will allow easier searching for the
failures.

Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/util.py

@@ -500,9 +500,9 @@ def log_failed_task(compose, variant, arch, deliverable, subvariant, logger=None
     ident = 'variant %s, arch %s' % (variant.uid if variant else 'None', arch)
     if subvariant:
         ident += ', subvariant %s' % subvariant
-    logger.info('[FAIL] %s (%s) failed, but going on anyway.' % (msg, ident))
+    logger.error('[FAIL] %s (%s) failed, but going on anyway.' % (msg, ident))
     if exc:
-        logger.info(str(exc))
+        logger.error(str(exc))
         tb = traceback.format_exc()
         logger.debug(tb)