slapgrid: Provide requested state in buildout

Add a requested-state entry in the slap-connection section set to the requested state of the computer partition being processed.

The slapos.cookbook:request recipe is supposed to propagate the state of the requesting instance to the requested instance, but this looks like it's currently broken: what slapos.cookbook:request does is it looks for a requested entry in slap-connection, but there currently seems to be none. So this MR could be used to fix state propagation to child instances.