Use distro agnostic way of install/update packages

[Garrett Holmstrom]

CloudConfig.install_packages and CloudConfig.update_package_sources could both be made more distro-agnostic by calling PackageKit's pkcon program instead of apt-get. It should be a drop-in replacement like so:

apt-get upgrade -> pkcon upgrade
apt-get install -> pkcon install
apt-get update -> pkcon refresh

AFAICT, pkcon's "-y" option is equivalent to passing "--force-confdef", "--force-confold" and "--assume-yes" to the appropriate programs. Passing "-p" to pkcon makes its output suitable for logging. Unfortunately there doesn't seem to be an option to silence its output completely, but its stdout could always be dropped.

[Garrett Holmstrom (gholms)]

An alternative to this is to instead come up with a common interface that package manager-specific backends can implement. There was a short IRC discussion about that, but so far nothing has happened toward that end.

[Joshua Harlow (harlowja)]

This might be a good top-level function for the distro class in 0.7.0 (using pkcon)

[James Falcon (falcojr)]

Distros now implement their own method of installing packages. There are no plans to change this.

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/2189