Removed cloud user private key pushing to nodes

  Due to security considerations we should not send private key of cloud
  users to VMs. This is mostly needed for Heat provisioning logic, where
  heat templates must not have secret keys written in user-data section.
  With this change Heat templates will look like as follows:
  http://paste.openstack.org/show/55008/

  Savanna old provisioning engine is also cleared from pushing private keys
  to nodes.

  Changed behaviour of wait_until_accessible method. Now it checks
  ~/.ssh/authoriszed_keys instead of ~/.ssh/id_rsa

  (NOTE: don't worry about code duplication in both engines). The common
  part of provisioning code will be extracted soon as part of bug
  https://bugs.launchpad.net/savanna/+bug/1259170

Change-Id: Ibe42cf6fc756ffc92bfc3fe520f4cecb732d858b
Closes-Bug: #1260357
Merge "Removed cloud user private key pushing to nodes"