create volumes in an organized directory structure

[Kunde21]

Feature adds the Controller Publish/Unpublish capability to the driver.

The root directory is already configurable, so that can be matched to a specific export on the moosefs cluster. We leverage the ability to set default storage class, trash time, and other settings on that directory to apply to all cluster volumes.

Within that root directory, a volumes directory will contain all of the volumes created for that cluster. Later, we will add a snapshots directory to hold those snapshots, alongside created volumes.

closes #1

[Kunde21]

Bolt was the wrong solution for tracking volumes.