Disable pkg_install output during upgrade

[Jonathan Perkin <jperkin%mnx.io@localhost>]

Hi,

This is a patch I've pushed to my binary package repositories, and while 
I don't intend to propose it for inclusion into pkgsrc just yet, it may 
be useful for others to include in their repositories.

Our upgrade process is effectively pkg_delete && pkg_add, and this means 
that any package that is either upgraded or refreshed will print both 
install and deinstall script messages, as well as output MESSAGE files, 
on every update.

At best this is annoying (users get spammed with the same messages 
telling them things they've already acted upon when first installing the 
packages), and at worst can end up with a broken system.  Consider the 
output a user sees when pkgin is updated:

  ===========================================================================
  The following files are no longer being used by pkgin-22.10.0nb1,
  and they can be removed if no other packages are using them:

        /opt/local/etc/pkgin/repositories.conf

  The following directories are no longer being used by pkgin-22.10.0nb1,
  and they can be removed if no other packages are using them:

        /opt/local/etc/pkgin
        /var/db/pkgin
  ===========================================================================

While many of us will know simply to ignore these messages, for newer 
users who aren't familiar with how things work they may legitimately 
think that these files and directories are no longer used (perhaps the 
package switched to a different directory and these are the obsolete 
locations?)  They act on what they are told, and now they have a broken 
system.

This patch turns off pkg_install stdout for any upgrades:

  https://github.com/TritonDataCenter/pkgsrc/commit/f4a4b80160f083abc2eb82c60bbc353b49f7e7d2

Explicit package installs or removals will continue to output INSTALL 
and DEINSTALL script messages, as well as show MESSAGE files, but for 
the general "pkgin upgrade" case this results in much cleaner output 
where errors will be significantly more visible.

Obviously it would be better to have proper upgrade handling in 
pkg_install, but that is a much larger project.

--
Jonathan Perkin   -   mnx.io   -   pkgsrc.smartos.org
Open Source Complete Cloud   www.tritondatacenter.com