provider/aws: AWS SpotFleet Requests now works with Subnets and AZs (#8320)
provider/aws: AWS SpotFleet Requests now works with Subnets and AZs (#8320)

* provider/aws: Change Spot Fleet Request to allow a combination of
subnet_id and availability_zone

Also added a complete set of tests that reflect all of the use cases
that Amazon document
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/spot-fleet-examples.html

It is important to note there that Terraform will be suggesting that
users create multiple launch configurations rather than AWS's version of
combing values into CSV based parameters. This will ensure that we are
able to enforce the correct state

Also note that `associate_public_ip_address` now defaults to `false` - a migration has been
included in this PR to migration users of this functionality. This needs
to be noted in the changelog. The last part of changing functionality
here is waiting for the state of the request to become `active`. Before
we get to this state, we cannot guarantee that Amazon have accepted the
request or it could have failed validation.

```
% make testacc TEST=./builtin/providers/aws
% TESTARGS='-run=TestAccAWSSpotFleetRequest_'
% 2 ↵
==> Checking that code complies with gofmt requirements...
/Users/stacko/Code/go/bin/stringer
go generate $(go list ./... | grep -v /terraform/vendor/)
2016/08/22 15:44:21 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v
-run=TestAccAWSSpotFleetRequest_ -timeout 120m
=== RUN   TestAccAWSSpotFleetRequest_changePriceForcesNewRequest
--- PASS: TestAccAWSSpotFleetRequest_changePriceForcesNewRequest (133.90s)
=== RUN   TestAccAWSSpotFleetRequest_lowestPriceAzOrSubnetInRegion
--- PASS: TestAccAWSSpotFleetRequest_lowestPriceAzOrSubnetInRegion (76.67s)
=== RUN   TestAccAWSSpotFleetRequest_lowestPriceAzInGivenList
--- PASS: TestAccAWSSpotFleetRequest_lowestPriceAzInGivenList (75.22s)
=== RUN   TestAccAWSSpotFleetRequest_lowestPriceSubnetInGivenList
--- PASS: TestAccAWSSpotFleetRequest_lowestPriceSubnetInGivenList (96.95s)
=== RUN   TestAccAWSSpotFleetRequest_multipleInstanceTypesInSameAz
--- PASS: TestAccAWSSpotFleetRequest_multipleInstanceTypesInSameAz (74.44s)
=== RUN   TestAccAWSSpotFleetRequest_multipleInstanceTypesInSameSubnet
--- PASS: TestAccAWSSpotFleetRequest_multipleInstanceTypesInSameSubnet (97.82s)
=== RUN   TestAccAWSSpotFleetRequest_overriddingSpotPrice
--- PASS: TestAccAWSSpotFleetRequest_overriddingSpotPrice (76.22s)
=== RUN   TestAccAWSSpotFleetRequest_diversifiedAllocation
--- PASS: TestAccAWSSpotFleetRequest_diversifiedAllocation (79.81s)
=== RUN   TestAccAWSSpotFleetRequest_withWeightedCapacity
--- PASS: TestAccAWSSpotFleetRequest_withWeightedCapacity (77.15s)
=== RUN   TestAccAWSSpotFleetRequest_CannotUseEmptyKeyName
--- PASS: TestAccAWSSpotFleetRequest_CannotUseEmptyKeyName (0.00s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/aws    788.184s
```

* Update resource_aws_spot_fleet_request.go

ashinohara/terraform-provider-aws,Ninir/terraform-provider-aws,Ninir/terraform-provider-aws,nbaztec/terraform-provider-aws,ClementCunin/terraform-provider-aws,ashinohara/terraform-provider-aws,Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,nbaztec/terraform-provider-aws,kjmkznr/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,nbaztec/terraform-provider-aws,ClementCunin/terraform-provider-aws,kjmkznr/terraform-provider-aws,Ninir/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,ClementCunin/terraform-provider-aws,ashinohara/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,ClementCunin/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,ashinohara/terraform-provider-aws,nbaztec/terraform-provider-aws