Better parsing for global ostree options

Better parsing for global ostree options

 * Specifying global options after the command for a more natural:
   # ostree commit --repo=/path/to/repo ...
 * Support asking for --help without --repo
   # ostree commit --help
 * Support short form of -h
 * Support specifying --repo without equals sign
   # ostree --repo /path/to/repo commit ...
 * Support global --help and -h
   # ostree --help
 * Ditto for ostree admin sub commands
 * Removed some leaky code

https://bugzilla.gnome.org/show_bug.cgi?id=705903