Node create api rework

Warning -- will require a Sledgehammer rebuild.

This exposes the internal machinery that Crowbar uses create nodes and
bind their initial noderoles, and fixes a deadlock exposed by the API rework.
Instead of POSTing to /api/v2/nodes and being handed back a fully fledged node, we now need a few different API calls:

* POST to /api/v2/nodes to create a basic Node object.  This will not
  have any roles bound to it nor will it have any addresses from the
  admin network assigned to it. The node will neither be alove nor available.
* (Optional) PUT any node-specific hints that may be needed for the
  bootstrap process, including node MAC addresses or your suggested IP
  address.
* POST to /api/v2/node_roles to bind default roles to the node.  Binding
  crowbar-admin-node will result in the node having all the roles needed
  for it to act as an admin node, and crowbar-managed-node will bind all
  the roles needed for the Sledgehammer discovery process to work.
* (Optional) PUT any node-specific attrib updates to the node.
* PUT to /api/v2/nodes/<node_name>/commit to move all the node's
  noderoles from PROPOSED to TODO, and mark the node as available (but
  still not alive)

The exposed deadlocks were resolved by:

* Rework the Jig exception management stuff to consolidate it even
  more.  Everything that needs to happen with a noderole to make a Jig
  do work now happens inside of delayed_jobs, and any exception will
  throw the noderole into ERROR.  This also zaps the added boilerplate
  that was added in the last jig rework.  The bulk of the change deals
  with the indentation changes for this work.
* Reworked all the locations that were calling Run.run! to ensure that
  Run.run! is never called inside of a transaction.  Going forward this
  invariant will be enforced by the Run.locked_transaction class method,
  which will throw an error if it is called inside another transaction.
* Changed the on_node_* hooks to be called via after_commit.  This
  makes it easier for hooks that need to call Run.enqueue to schedule
  will not inadvertently be inside a transaction.
* Add our own transaction methods that set the default transaction isolation level to repeatable_read, and that retry rollbacks due to serialization failures automatically.

This pull request also includes several fixups for excess serialization failures, a more useful logger that records the timestamp, PID, and log level of logged information, and the beginnings of the snapshot-ectomy.