[system_test]Plugin tests should be more configurable

[Tatyanka]

http://jenkins-product.srt.mirantis.net:8080/view/6.0_swarm/job/6.0_fuelmain.system_test.ubuntu.plugins/3/console

For now, only one variable PLUGIN_PATH is using for plugin tests, but we have several plugin in this group(like lbaas, example plugin). As result tests for lbaas and example plugin runs with wrong plugin.fp file and provide false result

So we need to update test:
Add Separate variable for each plugin (In those case 3 plugins will be downloaded by jenkins before run) and change places in code, where PLUGIN_PATH is using

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/141020

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/6.0
Review: https://review.openstack.org/141021

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/141020
Committed: https://git.openstack.org/cgit/stackforge/fuel-main/commit/?id=ab64a3d6fd2a3c4735b42007b2022a91e9345379
Submitter: Jenkins
Branch: master

commit ab64a3d6fd2a3c4735b42007b2022a91e9345379
Author: Tatyana Leontovich <email address hidden>
Date: Thu Dec 11 13:30:01 2014 +0200

    Add single path variable for each plugin

    To get possibility download 3 plugin during
    swarm tets we add single path variable
    for each plugin:
    * GLUSTER_PLUGIN_PATH
    * EXAMPLE_PLUGIN_PATH
    * LBAAS_PLUGIN_PATH

    Change-Id: Ic06bbcef9badbe99a9b2d81627f8070d9e8964f6
    Closes-Bug: #1401219

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/141021
Committed: https://git.openstack.org/cgit/stackforge/fuel-main/commit/?id=12ef78303559322129211bf3d1f0e645ba8f702e
Submitter: Jenkins
Branch: stable/6.0

commit 12ef78303559322129211bf3d1f0e645ba8f702e
Author: Tatyana Leontovich <email address hidden>
Date: Thu Dec 11 13:30:01 2014 +0200

    6.0 Add single path variable for each plugin

    To get possibility download 3 plugin during
    swarm tets we add single path variable
    for each plugin:
    * GLUSTER_PLUGIN_PATH
    * EXAMPLE_PLUGIN_PATH
    * LBAAS_PLUGIN_PATH

    Change-Id: Ic06bbcef9badbe99a9b2d81627f8070d9e8964f6
    Closes-Bug: #1401219