Nailgun enables all versions of plugins instead of one

[Evgeniy L]

Steps to reproduce:
1. install plugin "fuel_plugin_name" with version 1.0.0
2. install plugin "fuel_plugin_name" with version 2.0.0
3. install plugin "fuel_plugin_name" with version 0.1.0
4. create environment
5. enable plugin on UI

Actual result:
Nailgun enables all of the plugin versions instead of the latest plugin (2.0.0)
And sends tasks on installation for all 3 plugins

Expected result:
After cluster is created, user can enable a plugin, when plugin is enabled
Nailgun should use the latest version of plugin i.e. 2.0.0 and send
tasks only for this plugin.

VERSION:
  feature_groups:
    - mirantis
  production: "docker"
  release: "6.0"
  api: "1.0"
  build_number: "98"
  build_id: "2014-11-12_15-55-58"
  astute_sha: "3c374c9f7bfbdbcd7ce2f716cd704e3044e6fb41"
  fuellib_sha: "db708da56437210120fc1b41730b6fc55863481a"
  ostf_sha: "720cc1308c3a7081736edd167e7928ca61914aaa"
  nailgun_sha: "f481174170d54c4cf4c6495e3a9a2044af5f7183"
  fuelmain_sha: "144d62f990757cd17f4e75fd51e9b131e4238d20"

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/136574

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/136574
Committed: https://git.openstack.org/cgit/stackforge/fuel-web/commit/?id=00dcb899894e0a18d3fb3524f9882564c026c81f
Submitter: Jenkins
Branch: master

commit 00dcb899894e0a18d3fb3524f9882564c026c81f
Author: Evgeniy L <email address hidden>
Date: Fri Nov 21 21:25:16 2014 +0400

    In case of several plugins, nailgun should use the newest

    For example Fuel has 3 plugins:
    - name: plugin_name, version: 1.0.0
    - name: plugin_name, version: 2.0.0
    - name: plugin_name, version: 0.1.0

    The problem was, when user enables a plugin on UI,
    Nailgun enables all of the installed plugins.

    With this patch, after user creates environment he can
    enable or disable only 2.0.0 version of plugin.

    If after environment creation, new version of the plugin
    is installed, user cannot use this new version, he
    should create new environment in order to enable it.

    Change-Id: I51ba03166cd2a7379c6f0912d668265bf88a316d
    Closes-bug: #1395342