[FC-20956] batou_ext.fcio: Add components that set an RG in maintenance for the time of the deployment

[Ma27]

Given a provision section in the secret config like

[provision]
project = test
api_key = <redacted>

an environment config like this

[host:test42]
components =
  demo
  directoryxmlrpc
  maintenancestart
  maintenanceend

and a component like this

class Demo(Component):
  def configure(self):
    self.provide("needs-maintenance", self)
    self += File("foobar")

then all subcomponents configured by `Demo will be deployed while the RG is in maintenance.

[Ma27]

I guess a bit more docs would be nice. But first we should discuss the things below.

[Ma27]

This has the downside that setting it up is a little verbose: you have to add three additional components.
We may be able to cut it down to two by removing the DirectoryXMLRPC and setting up the client in each component.

Another idea I had was to use a decorator which injects Start end End into a component (and calls the component's configure in between), but this has the downside that the maintenance is left when the component itself is updated. I.e.

@needs_maintenance
class Foobar(Component):
  def configure(self):
    # The RG is in maintenance when X & Y are deployed
    self += X()
    self += Y()
  def update(self):
    # when this is reached, we're not in maintenance anymore.

Thoughts?

[Ma27]

I effectively assume here that each host in a deployment is in the same RG.
Do we even have cases where this is not True?

[Ma27]

I still have bad feelings about this: every deployment with no other change will set the RG to maintenance for a short time with this.

Unfortunately I don't have a better idea after reading through batou's sources: when MaintenanceStart is deployed, we don't know yet if anything else will change later that needs maintenance. We could of course run all of the verify() methods of these components in here, but this doesn't take their sub-components into account.

Ideas? Or is this good enough?