Provide docstrings for horizon tables DeleteAction

While it's true that the `horizon.tables.actions.DeleteAction`
code is self explanatory (and hence documentation on its own),
the motivation behind this was to replace """Doc missing.""" with
something more descriptive that will show up at:-
http://docs.openstack.org/developer/horizon/ref/tables.html#horizon.tables.DeleteAction

It would also be good to call `help(DeleteAction)` to get a decent
description of the class.

Change-Id: Ib1198711589ac704278db53d4d53fd655146aaa9
Fix network select widget for launching instances

This fixes the problem where the Networking tab of the Launch
Instance panel does not work if there is more than one network.
Also fixes the similar widget used for firewall rules.

Change-Id: Ied5a800bf8cec7c846c28149d732f769af56f354
Closes-Bug: 1352775
Merge "Fix network select widget for launching instances"
Merge "Provide docstrings for horizon tables DeleteAction"