CRUD for "Before End" lease notification timeframe

Currently some events (start,end) can be modified via using lease-update. Do you want to implement mechanism of direct events modification?

[casanch1] With this bp: https://blueprints.launchpad.net/climate/+spec/notifications it was introduced a new kind of event: "Before End", to send a notification x hours before the lease expires. That bp implementation uses a configuration option for the x value.
The goal of this BP is to give the option in the API to define the x hours while creating the Lease. And moreover, when a lease is modified we should also give that option.

[db] ok, nice - will you work on

[casanch1] Sure, I can work on this.

[cmart] Regarding the blazar client changes, we need to add a new parameter for the lease-update command. Since both prolong-for and reduce-by parameter work with elapsed time, I suggest that the same should apply to this new field. What do you think? ElapseD time or fixed date?

[cmart] How do you propose to do the delete operation for this new event?

[casanch1] What do you mean with the delete operation? If it is the delete of the lease, then we just need to leave the current implementation as it is. But if you mean to delete only the before_end_lease event, then I think this should not be supported.

Gerrit topic: https://review.openstack.org/#q,topic:bp/before-end-notification-crud,n,z

Addressed by: https://review.openstack.org/89833
    API Support for before_end param configuration

Addressed by: https://review.openstack.org/92177
    Update V2 documentation

Work items:
Blazar documentation changes to reflect new parameter: INPROGRESS
Blazar Manager changes on lease update and lease create functions: DONE
Blazar-Client changes to add new parameter to lease-update command: POSTPONED