Improve MAAS images-import processes

  * Add check,that rackd finished bss sync
    Unfortunatly, those check for now,possible only for all nodes
  * Add a workaround for adding bss.
    Maas doesn't have a possibility to check the stream-info import status.
    On slow systems\network, boot-source may be added, but information from
    it may not be imported yet.
    A 400 error raises when trying to configure bss for such boot source
    endpoint.
  * TODO: maas formula requires refactor.
    Current implementation doent care about service separation, aka
    Region|rack controller|proxy|dhcpd deployments on different nodes and
    related management. Like example - not possible to chose /different/
    rack controller to process.

Closes-Bug: PROD-20858 (PROD:20858)

Change-Id: I8875cdb30e7db735db210412c4357da95fe8e320
3 files changed