Don't store full certificate data in state file (Fixes: #156).

[andrewsomething]

$ make testacc TESTARGS='-run=TestAccDigitalOceanCertificate_Basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test $(go list ./... |grep -v 'vendor') -v -run=TestAccDigitalOceanCertificate_Basic -timeout 120m
?   	github.com/terraform-providers/terraform-provider-digitalocean	[no test files]
=== RUN   TestAccDigitalOceanCertificate_Basic
--- PASS: TestAccDigitalOceanCertificate_Basic (21.16s)
PASS
ok  	github.com/terraform-providers/terraform-provider-digitalocean/digitalocean	21.181s

[zachgersh]

Seems good to me!

Side note, do we understand why amazon terraform resource is doing this:
https://github.com/terraform-providers/terraform-provider-aws/blob/69f3f6069ea648022017c6aa9f49dd7bc2a9c418/aws/resource_aws_iam_server_certificate.go#L233

[andrewsomething]

@zachgersh Found the original issue and commit:

hashicorp/terraform#3837
hashicorp/terraform-provider-aws@1ed4e49

Seems like Windows style line ending were causing unintentional diffs to be generated. Using the cert material from their tests, it looks like the DO API will not even accept a cert with them.

Using this:

https://raw.githubusercontent.com/terraform-providers/terraform-provider-aws/1ed4e4933b5d8b7e66450162f638d08df8c27333/test-fixtures/iam-ssl-windows-line-endings.pem

the API fails with:

Error creating Certificate: POST https://api.digitalocean.com/v2/certificates: 422 (request "a016ee5d-9271-4376-9699-a431c0bfa218") Invalid certificate data rpc error: code = InvalidArgument desc = The provided certificate or private key is not a valid PEM block

Stripping the CRs, the resulting cert works:

cat iam-ssl-windows-line-endings.pem |  tr -d '\r' > iam-ssl-windows-line-endings-1.pem

So I'd guess that IAM Server is stripping these itself.