Testing of OSCI packages on a stable environment

1. Enables the 'custom_repo' decorator which add new rpm/deb
packages to FUEL master node from custom repository before
OS cluster is created. Can be used with any system test.

2. In case of deployment error, checks the puppet logs
in /var/log/docker-logs/remote/node-*/ for unmet dependences
of packages which are failed to install during deployment.

Use the following environment variables:
* required:
  CUSTOM_PKGS_MIRROR=<URL to repository>

Example:
========
export CUSTOM_PKGS_MIRROR
CUSTOM_PKGS_MIRROR=http://osci-obs.vm.mirantis.net:82/centos-fuel-master-17831/centos

sh -x utils/jenkins/system_tests.sh -t test -w ...\
      -V ... -j ... -i ... -o --group=bvt_2
========

Implements: blueprint testing-packages-in-enviroment

Change-Id: Iafdbe13760b4d1412fc2b067d0687a29dc5f6380
(cherry picked from commit 8724bab1a8e87a558c9624c350e8f55dc59139c3)