provider/template: convert resources to data sources

[apparentlymart]

The template resources don't actually need to retain any state, so they are good candidates to be data sources.

[apparentlymart]

@phinze / @jen20: now that the bugs around testing data sources have been resolved this seems to work as expected, so I think it's now ready for review.

[ColinHebert]

Fixes #6899

[jen20]

After rebase:

make testacc TEST=./builtin/providers/template
==> Checking that code complies with gofmt requirements...
/Users/James/Code/go/bin/stringer
go generate $(go list ./... | grep -v /terraform/vendor/)
2016/07/08 17:11:37 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/template -v  -timeout 120m
=== RUN   TestRender
--- PASS: TestRender (0.06s)
=== RUN   TestTemplateRendering
--- PASS: TestTemplateRendering (0.08s)
=== RUN   TestValidateTemplateAttribute
--- PASS: TestValidateTemplateAttribute (0.00s)
=== RUN   TestTemplateSharedMemoryRace
--- PASS: TestTemplateSharedMemoryRace (0.00s)
=== RUN   TestProvider
--- PASS: TestProvider (0.00s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/template   0.151s

[jen20]

LGTM! I'll merge this locally following the rebase and push it up.

[jen20]

Merged as 861ac53.

[ghost]

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