[git_trace2] Add logs for critical cmds

Trace logs emitted from repo are not useful on error for many critical
commands. This change adds errors for critical commands to trace logs.

Change-Id: Ideb9358bee31e540bd84a94327a09ff9b0246a77
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/373814
Reviewed-by: Joanna Wang <jojwang@google.com>
Tested-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

subcmds/rebase.py

@@ -206,7 +206,9 @@ branch but need to incorporate new upstream changes "underneath" them.
                     ret += 1
 
         if ret:
-            out.fail("%i projects had errors", ret)
+            msg_fmt = "%d projects had errors"
+            self.git_event_log.ErrorEvent(msg_fmt % (ret), msg_fmt)
+            out.fail(msg_fmt, ret)
             out.nl()
 
         return ret