discover: check package status before trying to install/update it

Summary:
With latest changes to packagekit, it may now return more packages from 'pkcon get-updates' command with new statuses: "removed" or "obsoleted". This change is needed to filter such packages since Discover is using list of packages similar to the output of mentioned command but ignores package statuses. Otherwise, Discover would try to install all packages, including removed and obsoleted, and fail while trying to resolve such transaction due to package conflicts, if there are such packages present.

packagekit changes:
https://github.com/hughsie/PackageKit/pull/341

Reviewers: jriddell, apol

Reviewed By: apol

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D24653