plugins cannot be removed even if the environment was reset

[Alex Schultz]

Once a plugin has been enabled, it seems that it can no longer be removed even if the environment is reset and the roles are no longer in use.

Steps to reproduce:
1. install a plugin
2. attempt to deploy with plugin (add the role to a node)
3. stop deployment
4. reset environment
5. remove role from node
6. uncheck plugin from settings page
7. attempt to remove plugin via cli
8. error indicating plugin is still in use

[root@nailgun ~]# fuel plugins --remove fuel-plugin-etckeeper==1.0.0
400 Client Error: Bad Request (Can't delete plugin which is enabled for some environment.)

Expected results:
Plugin should be able to be removed if it is no longer configured

Actual results:
Plugin cannot be removed as it is still claiming to be in use.

VERSION:
  feature_groups:
    - mirantis
  production: "docker"
  release: "8.0"
  api: "1.0"
  build_number: "283"
  build_id: "283"
  fuel-nailgun_sha: "073beb9f02e103e8f78abe9425d4c9feb5fab6e4"
  python-fuelclient_sha: "f96659066e522e28b389de3cc685f6f2aacca3da"
  fuel-agent_sha: "2f18b7596bc7da79d2f28c34f42620b2090d8a35"
  fuel-nailgun-agent_sha: "a33a58d378c117c0f509b0e7badc6f0910364154"
  astute_sha: "f7df18ab6b2089649abcfa8cf667ffd6b332be1a"
  fuel-library_sha: "66fc43373039a23fb63c26e7919a60b3560e0db1"
  fuel-ostf_sha: "632730169e8c01afe7fd5d78a898f00d4646358b"
  fuel-mirror_sha: "31b9df814960ec69b644ca9b689dacec0c7e10a1"
  fuelmenu_sha: "680b720291ff577f4c058cee25f85e563c96312e"
  shotgun_sha: "a0bd06508067935f2ae9be2523ed0d1717b995ce"
  network-checker_sha: "a3534f8885246afb15609c54f91d3b23d599a5b1"
  fuel-upgrade_sha: "1e894e26d4e1423a9b0d66abd6a79505f4175ff6"
  fuelmain_sha: "1577a306c2c9e7bd12f28c0e16cf3652997da004"

Here's a basic plugin that was I was able to reproduce this with, https://github.com/mwhahaha/fuel-plugin-etckeeper

[Fedor Zhadaev (fzhadaev)]

Cannot reproduce bug. After provided steps plugin deleted successfully.

VERSION:
  feature_groups:
    - mirantis
  production: "docker"
  release: "8.0"
  api: "1.0"
  build_number: "429"
  build_id: "429"
  fuel-nailgun_sha: "12b15b2351e250af41cc0b10d63a50c198fe77d8"
  python-fuelclient_sha: "4f234669cfe88a9406f4e438b1e1f74f1ef484a5"
  fuel-agent_sha: "df16d41cd7a9445cf82ad9fd8f0d53824711fcd8"
  fuel-nailgun-agent_sha: "92ebd5ade6fab60897761bfa084aefc320bff246"
  astute_sha: "c7ca63a49216744e0bfdfff5cb527556aad2e2a5"
  fuel-library_sha: "3eaf4f4a9b88b287a10cc19e9ce6a62298cc4013"
  fuel-ostf_sha: "214e794835acc7aa0c1c5de936e93696a90bb57a"
  fuel-mirror_sha: "b62f3cce5321fd570c6589bc2684eab994c3f3f2"
  fuelmenu_sha: "85de57080a18fda18e5325f06eaf654b1b931592"
  shotgun_sha: "63645dea384a37dde5c01d4f8905566978e5d906"
  network-checker_sha: "9f0ba4577915ce1e77f5dc9c639a5ef66ca45896"
  fuel-upgrade_sha: "616a7490ec7199f69759e97e42f9b97dfc87e85b"
  fuelmain_sha: "e8e36cff332644576d7853c80b8a53d5b955420a"