Remove nodes constraint on provisioning task

[Alexandr Kostrikov]

Detailed bug description:
There is possibility to run provision without node, assuming we have a cluster without nodes:
`self.fuel_web.provisioning_cluster_wait(cluster_id)`

It builds image which can be used later to speedup provisioning (especially for tests with snapshots reverts)

But after image is build it fails with

2016-04-15 14:00:59 INFO [31404] a43874a3-ff7f-45d1-bb7b-41cb017744e2: stdout: stderr: Warning: Permanently added '10.109.0.2' (ECDSA) to the list of known hosts.
     exit code: 0
2016-04-15 14:00:59 INFO [31404] Provision summary: time was spent 00:16:53
2016-04-15 14:00:59 ERROR [31404] Error running provisioning: Nodes to provision are not provided!, trace:
["/usr/share/gems/gems/astute-9.0.0/lib/astute/provision.rb:38:in `provision'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/orchestrator.rb:127:in `provision'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/server/dispatcher.rb:51:in `provision'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/server/dispatcher.rb:37:in `image_provision'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/server/server.rb:187:in `dispatch_message'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/server/server.rb:146:in `block in dispatch'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/server/task_queue.rb:64:in `call'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/server/task_queue.rb:64:in `block in each'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/server/task_queue.rb:56:in `each'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/server/task_queue.rb:56:in `each'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/server/server.rb:144:in `each_with_index'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/server/server.rb:144:in `dispatch'",
 "/usr/share/gems/gems/astute-9.0.0/lib/astute/server/server.rb:121:in `block in perform_main_job'"]

2016-04-15 14:00:59 DEBUG [31404] Dispatching aborted by image_provision

It would be really helpful to prepare image before deployment.

[Bug Checker Bot (bug-checker)]

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[Alexandr Kostrikov (akostrikov-mirantis)]

Actually, it is better to create task
prepare_ubuntu_image_for_release

Because in 90% of cases we use release settings for ubuntu image.

[Dmitry Pyzhov (dpyzhov)]

We passed SCF for 9.0. Moving the bug to 10.0