Add support for local storage

[stgraber]

When initializing a MicroCloud, local storage should be offered prior to setting up remote storage.

The updated microcloud init process should therefore be:

• Bootstrap
• Detect and join other servers
• Ask whether the user wants to setup local storage, if yes
  • Check that we have at least one available disk per server
  • Ask the user to select exactly one disk per server
• Ask whether the user wants to setup remote storage, if yes
  • Check that we have at least three disks spread across at least three servers
  • Ask the user to select what disks to include into Ceph
• If local storage was chosen, use it for the default profile, otherwise use remote (if was setup)

[masnax]

Closed by #37