Add ability to download files to 7.0.custom_system_test

[Maksym Strukov]

Our plugins system tests accept path to plugins in env var. In order to add ability to do plugin tests custom run we need following changes in 7.0.custom_system_test job:

* new field defined "plugins", where user can put few urls to files with comma delimeter;
* job will parse urls from field and download all file to some folder preserving the filename;
* path to download folder will be pre-defined and written in field comment

In result it's expected that user can put plugins urls to this field, and knowing the names of the files and download directory, put pathes to ADDITIONAL_PARAMETERS as env variables for system tests.

[Aliaksei Cherniakou (acherniakou)]

Follow up our call with Maksym:
- it was decided to update both 7.0 and 8.0 custom_system_test jobs;
- new text field PLUGINS is to be added, where URLs to plugins will be placed one by line;
- new string field PLUGINS_DIR is to be added with absolute path to the directory to download the plugins to. Default value: $WORKSPACE/downloaded_plugins .

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

Related fix proposed to branch: master
Change author: Aliaksei Cherniakou <email address hidden>
Review: https://review.fuel-infra.org/13885

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

Reviewed: https://review.fuel-infra.org/13885
Submitter: Aleksandra Fedorova <email address hidden>
Branch: master

Commit: 4ddb8133942fc84725f630fa3c3e6f2087a30c9e
Author: Aliaksei Cherniakou <email address hidden>
Date: Mon Nov 30 12:54:25 2015

Add possibility to download plugins providing URLs

This is done to provide ability to run plugins tests
against a custom set of plugins (by providing URLs list).
It affects 7.0.custom_system_test and 8.0.custom_system_test jobs.

The following fields have been added:
* text field PLUGINS where URLs to download should be
  provided one by line.
* string field PLUGINS_DIR to define absolute path to the
  directory where plugins will be stored after downloading.
  Its default value is $WORKSPACE/downloaded_plugins

Download functionality implemented via wget call in a simple
shell script using PLUGINS and PLUGINS_DIR values.

Change-Id: I48380d6482f1010d0c18d0f313835677aaaf3175
Related-Bug: #1483803

[Maksym Strukov (unbelll)]

It works http://jenkins-product.srt.mirantis.net:8080/view/custom_iso/job/8.0.custom_system_test/734/consoleFull