8.0-pkg-repotest-ubuntu test fails because of removing the rest of MidoNet plugin from Neutron tree

[Sergii Rizvan]

Detailed bug description:
 8.0-pkg-repotest-ubuntu test fails in the CR https://review.fuel-infra.org/#/c/22128/ where we remove Midonet plugin with the following error:

2016-06-20 14:26:54,706 ERROR Package "neutron-plugin-midonet" is not installable:
2016-06-20 14:26:54,706 ERROR Reading package lists...
Building dependency tree...
Reading state information...
Package neutron-plugin-midonet is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'neutron-plugin-midonet' has no installation candidate

For some reason pkg-repotest job tries to install neutron-plugin-midonet package after removing it from specs.

Steps to reproduce:
 Run 8.0-pkg-repotest-ubuntu against the CR https://review.fuel-infra.org/#/c/22128/
Expected results:
 8.0-pkg-repotest-ubuntu test passes
Actual result:
 8.0-pkg-repotest-ubuntu test fails
Reproducibility:
 Always
Workaround:
 No
Impact:
 The bug prevents merging the fix in https://review.fuel-infra.org/#/c/22128/
Description of the environment:
 Versions of components: 8.0

[Fuel Devops McRobotson (fuel-devops-robot)]

Fix proposed to branch: master
Change author: Alexander Tsamutali <email address hidden>
Review: https://review.fuel-infra.org/22289

[Fuel Devops McRobotson (fuel-devops-robot)]

Reviewed: https://review.fuel-infra.org/22289
Submitter: Ivan Remizov <email address hidden>
Branch: master

Commit: 23a26af7ec603c00cb022c1bae5dfd5f17b9b8bf
Author: Alexander Tsamutali <email address hidden>
Date: Tue Jun 21 13:17:30 2016

Do not try to install pinned/excluded packages in repo test

Currently repo-test-deb/repo-test-rpm try to install package even
if it was removed from control or spec file.

`generate_preferences`/`generate_excludes` are pinning/excluding
packages that were removed in CR. They will now return list of
pinned/excluded packages. These packages will be removed from
list of Mirantis packages that we are trying to test, because
they can not be installed.

Change-Id: If59687fba8e8f0f8dbf98f1f7bb52f7de8f578d1
Closes-Bug: #1594429