Fix event log command event hierarchy.

command should be cmd_name, to match what git is emitting. This also
fixes arguments, so that only relevant arguments are passed instead
of the entire sys.args, which will contain wrapper information

Change-Id: Id436accfff511292ec2c56798fffb2306dda38fc
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/443741
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Tested-by: Josip Sokcevic <sokcevic@google.com>

main.py

@@ -357,7 +357,7 @@ class _Repo:
         start = time.time()
         cmd_event = cmd.event_log.Add(name, event_log.TASK_COMMAND, start)
         cmd.event_log.SetParent(cmd_event)
-        git_trace2_event_log.StartEvent()
+        git_trace2_event_log.StartEvent(["repo", name] + argv)
         git_trace2_event_log.CommandEvent(name="repo", subcommands=[name])
 
         def execute_command_helper():