Add custom layout partitioning

  * In case of 'non-clean' partitioning, we may stuck in 400 error from MAAS
    The  RC of such issue, that we trying to apply totally custom schema, to
    any auto-predefined(or not cleaned previosly)
  * Add new layout: custom - which means, drop everything befere start part.
  * Misc: remove broken and unused func `create_partition_filesystem`

Closes-Bug: PROD-20317 (PROD:20317) 

Change-Id: I574c669616b9318b8ecafaf9c8ad4162c01b44e1
3 files changed