Report which part files failed log sorting in the CHECK

Before, the error wasn't informative enough to tell anyone what the
offending part file was for further inspection.  Now it is easier to dig
in and figure out why something is corrupted.

Change-Id: Ia8ca94c42495c7b6e9ac23f7bc325dd5ffd139b6
Signed-off-by: Austin Schuh <austin.schuh@bluerivertech.com>
diff --git a/aos/events/logging/logfile_sorting.cc b/aos/events/logging/logfile_sorting.cc
index 17eda4e..59cba17 100644
--- a/aos/events/logging/logfile_sorting.cc
+++ b/aos/events/logging/logfile_sorting.cc
@@ -267,9 +267,11 @@
     }
 
     if (configuration_sha256.empty()) {
-      CHECK(log_header->message().has_configuration());
+      CHECK(log_header->message().has_configuration())
+          << ": Failed to find header on " << part;
     } else {
-      CHECK(!log_header->message().has_configuration());
+      CHECK(!log_header->message().has_configuration())
+          << ": Found header where one shouldn't be on " << part;
     }
 
     // Looks like an old log.  No UUID, index, and also single node.  We have