praefect: Don't overwrite '-older-than' flag
Currently the list-untracked-repositories
subcommand fails to honor
the value passed in the -older-than
flag. This is due to our calling
cmd.FlagSet()
again after args have been parsed, resetting
cmd.onlyIncludeOlderThan
back to its default value.
Resolve this by getting the subcommand name from the already parsed flags passed in.
Fixes #4294 (closed)