Provide a mechanism for capturing package_command output

[Craig Tracey]

We have run into a few scenarios where yum fails to install certain packages via cloud-init. As all of the package_command implementations set capture=False when shelling out, there is no easy way for a user to debug this sort of a problem.

I am proposing that we add a directive that would selectively turn on logging for package_command.

[Scott Moser (smoser)]

ctracey, is there some reason why you'd not want 'tee' ?
as in
  output: {all: '| tee -a /var/log/cloud-init-output.log'}
the package command being logged makes quite reaosnable sense but is thre a
reason that capturing output generically is insufficient ?

[Scott Moser (smoser)]

marking fix-released. if you feel otherwise, please re-open and give comment as to why.

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/2403