gnu: kwindowsystem: Fix some test-cases (test-suite still disabled).

Make five tests pass, three are still failing – thus the test-suite is still
disabled. This commit's aim is to retain the progress.

* gnu/packages/kde-frameworks.scm (kwindowsystem)[native-inputs]: Add dbus.
  [arguments]<#:test?>: Change comment. <#:phases>: Replace phase `check` by
  new one befind 'install'.