* Fix invalid MIME formatting in multipart cloudinit userdata
Per https://tools.ietf.org/html/rfc822#appendix-B.2, MIME headers and Body need to be separated by two new lines (or CRLFs in this case).
The email parser in python can handle this which is what cloud-init uses but this bug causes problems if you try to parse the multipart message by languages other than python.
* Fix test cases
Fixes an uncaught panic during an interface cast in the `template_cloudinit_config` data source.
Fixes: #13572
```
$ make test TEST=./builtin/providers/template TESTARGS="-v -run=TestRender_handlePanic"
==> Checking that code complies with gofmt requirements...
==> Checking AWS provider for unchecked errors...
==> NOTE: at this time we only look for uncheck errors in the AWS package
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/04/12 10:46:33 Generated command/internal_plugin_list.go
go test -i ./builtin/providers/template || exit 1
echo ./builtin/providers/template | \
xargs -t -n4 go test -v -run=TestRender_handlePanic -timeout=60s -parallel=4
go test -v -run=TestRender_handlePanic -timeout=60s -parallel=4 ./builtin/providers/template
=== RUN TestRender_handlePanic
--- PASS: TestRender_handlePanic (0.00s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/template 0.028s
```
The template resources don't actually need to retain any state, so they
are good candidates to be data sources.
This includes a few tweaks to the acceptance tests -- now configured to
run as unit tests -- since it seems that they have been slightly broken
for a while now. In particular, the "update" cases are no longer tested
because updating is not a meaningful operation for a data source.
Devin Lundberg