Add provision_updated_at field to nodes table

For timeouts handling we need track time when deploy operations
started. This patch add new DateTime field 'provision_updated_at'
to nodes table. update_node() DB API method set this field when
provision state of a node changed.

Change-Id: I0c3dbd5164a8decead2a94449b5717cdd4a1f7a4
Merge "Add provision_updated_at field to nodes table"