vzlist: Short -e is for long --help

Signed-off-by: Pavel Emelyanov <xemul@sacred.ru>
vzlist: Spelling and arg name for --output

Signed-off-by: Pavel Emelyanov <xemul@sacred.ru>
yoda: Don't print names of option groups if only one group exists

Signed-off-by: Pavel Emelyanov <xemul@sacred.ru>
yopts: Mark yopt_print as printf-like function

Signed-off-by: Pavel Emelyanov <xemul@sacred.ru>