CLI pkg interface for package installation/removal

[gronke]

The ioc cli command allows installing and removing packages in started or stopped jails without requiring network.

The current CLI implementation has similarities to the pkg command, but does not use the same syntax. Installation and removal are implemented as shown here:

# install
ioc pkg <JAIL> <packages>

# remove
ioc pkg <JAIL> -r <packages>

It would be nice to find a more intuitive interface. Maybe forcing explicit usage of --remove/-r or --install/-i flag leads to a more consistent interface.

ioc pkg <JAIL> --install <packages>
ioc pkg <JAIL> --remove <packages>