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>