fuel2 update don't validate value of --repos argument

[Artem Hrechanychenko]

Detailed bug description:
 fuel2 update command has --repos argument, where we describe repository for MU installing. This repo need to be taken from repos list described in cluster attributes. And fuel2 update don't validate - this repo exist or not. If we run command with --repos wrong_repo_name - cluster updating process will be started successfully and we got error only from puppet.
So need to add checker to fuel2 update, and retrive list of cluster repos, and check "if --repo repos in cluster_repo_list"

Steps to reproduce:
 1)Any 9.0 env
 2)update 9.0 master and prepare for update 9.0 env via official instruction
 3) run "fuel2 update install --env {env_id} --repos wrong_repo --restart-rabbit --restart-mysql

Expected results:
 Cannot find wrong_repo in your cluster repos

Actual result:
 command successfully executed and deployment task started

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

Fix proposed to branch: 9.0
Change author: Denis V. Meltsaykin <email address hidden>
Review: https://review.fuel-infra.org/29772

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

Reviewed: https://review.fuel-infra.org/29772
Submitter: Pkgs Jenkins <email address hidden>
Branch: 9.0

Commit: 7f9a91c7a6166e3fb00a36602a389cb6fa60746a
Author: Denis V. Meltsaykin <email address hidden>
Date: Wed Jan 11 14:12:11 2017

[0.1.9] Repositories validation

The update tool now includes the validation of the repositories entered
by a user against the repositories available on a particular
environment. This fix also includes check that default repositories are
available on the environment.

        From: https://github.com/avgoor/python-cudet
        Commmit: 329a86efefe7e159e4ee3cc2d21a072fd2216c04

Change-Id: I9932035a83bff2313a104d3cfaedd3ea9d1b20aa
Closes-Bug: #1630170

[Dmitry Belyaninov (dbelyaninov)]

[root@nailgun ~]# fuel2 update install --env 1 --repos wrong_repo --restart-rabbit --restart-mysql
Invalid repository list: wrong_repo, valid repositories are: ubuntu-2, mos9.2-holdback, ubuntu-0, ubuntu-1, Auxiliary, mos, mos9.2-updates, mos-holdback, mos9.2-security, mos-proposed, mos-security, mos-updates
[root@nailgun ~]#

9.x snapshot #796