[QENG-3919] Make vmpooler checkouts be all or nothing (#153)

* (QENG-3919) spike for implementation of all-or-nothing checkout

* Fix two botched variable references

* Aggregate API helper methods

* Add specs for failed multi-vm allocation API endpoints

* (QENG-3919) Add tests for multiple vm requests

* (QENG-3919) Add (failing) specs for POST /vm/pool1+pool2 usages

This exposes the old (bad) behavior on this other code path. Will fix this up next.

* (QENG-3919) Bring query params version in line with JSON post version

Not clear to me why these had to be implemented so differently.

* (QENG-3919) extract common method from both methods of VM allocation

* (QENG-3919) Naming fix, cosmetic cleanups

I mean, I presume all these commits are going to get squashed away on merge anyway.

* (QENG-3919) Update API docs

We consider it a bug that the actual behavior was not this behavior, but the
documentation was also silent on this point.

* (QENG-3919) minor readability tweak in refactored method

* (QENG-3919) Clean up interim comments re: status codes

* (QENG-3919) Drop now-orphaned `checkout_vm` method

We kept this up-to-date while we were upgrading and refactoring, but, turns out,
this method is no longer called anywhere.  💀 🔥

* (QENG-3919) Return 503 status on failed allocation

Making sure we go back to the original functionality, which was:

 - status 200 when vms successfully allocated
 - status 404 when a pool name is unknown
 - status 404 when no pool name is specified
 - status 503 when vm allocation failed

* (QENG-3919) add net-ldap to Gemfile

Maybe we shouldn't foil-ball gems onto servers.

* (QENG-3919) Turns out, spush isn't a redis command

And hence we see once again the weakness of mockist tests.

* (QENG-3919) Pin the net-ldap gem to 0.11 for the jrubies, etc.

* (QENG-3919) Correct an old spelling error in spec descriptions

* (QENG-3919) Further tweak net-ldap version

* (QENG-3919) return_single_vm -> return_vm_to_ready_state

cc @shermdog

Gemfile

@@ -6,6 +6,7 @@ gem 'rake', '>= 10.4'
 gem 'rbvmomi', '>= 1.8'
 gem 'redis', '>= 3.2'
 gem 'sinatra', '>= 1.4'
+gem 'net-ldap', '<= 0.12.1' # keep compatibility w/ jruby & mri-1.9.3
 
 # Test deps
 group :test do