StorageHost table

[ketiltrout]

The StorageNode.address and StorageNode.username columns aren't really node-specific, but rather specific to the host on which they are located.

From an object-oriented point of view, we should create a new StorageHost table to record these per-host:

def StorageHost(base_model):
    name = pw.CharField(max_length=64, unique=True)
    username = pw.CharField(max_length=64, null=True)
    address = pw.CharField(max_length=255, null=True)

then delete StorageNode.address and StorageNode.username, and convert StorageNode.host into a reference to that table.

Can't be done while we're still running alpenhorn-1, though.