provider/aws: Fix AMI creation from snapshot issue

[grubernaut]

Previously the AMI creation accepted a static value for the AMI's block device's volume size.
This change allows the user to omit the volume_size attribute, in order to mimic the AWS API behavior, which will use the EBS Volume's size.

Also fixes a potential panic case when setting iops on the AMI's block device.

The aws_ami resource previously didn't have any acceptance tests, adds two acceptance tests and a full testing suite for the aws_ami resource, so further tests can be written, as well as expansion upon the other aws_ami_* acceptance tests

$ make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSAMI_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/02/09 20:18:22 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSAMI_ -timeout 120m
=== RUN   TestAccAWSAMI_basic
--- PASS: TestAccAWSAMI_basic (44.21s)
=== RUN   TestAccAWSAMI_snapshotSize
--- PASS: TestAccAWSAMI_snapshotSize (45.08s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/aws    89.320s

Fixes: #11655

[stack72]

Nice work - would rather the code on line 65 was deleted than commented out though. But that's just a nit pick!

[CarltonHenderson]

Awesome @grubernaut. Thanks for fixing this - and even adding tests :-). This makes my life so much happier.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.