pkg uses "is stdin a terminal?" to decide if it's running interactively
and thereby whether it should display a progress bar during downloads.
While rc.d scripts have a terminal attached, for the common case of
unattended installation of servers, this script is not being used
interactively; so redirect stdin from /dev/null to silence the progress
bars and reduce console spew.
The -q option could be used to accomplish this, but that would also
eliminate other more useful information, such as the names and versions
of packages being installed.