Add the 'nan' module needed by the new 'authenticate-pam'

Change-Id: I1bd53c031533b92f7d5b8de10fb8d7d145b3d470
Add CLI command to associate users with data volumes

* Updated user schema to include a volume id field
* Added CLI command that sets a user's volume id to a particular value
* Stubbed out a command for automatically creating and associating a
  volume with a user. Doesn't do anything yet.
* Did NOT add any code yet that uses the data volume id for anything.
  It only updates the database.

Change-Id: I58f1bbe4a38807b9ae68d64506a4ced209fbadb2