provider/google: Add google_compute_zones data source

[radeksimko]

I wanted to build a GKE cluster and I saw hard-coded zones in the example which is what prompted me to write this data source in the 1st place.

There are some HCL changes that would help making this more elegant/useful though, specifically slicing lists via colon, e.g.

zone = "${data.google_compute_zones.available.names[0]}"
additional_zones = [
    "${data.google_compute_zones.available.names[1:]}"
]

---

Test plan

make testacc TEST=./builtin/providers/google TESTARGS='-run=TestAccGoogleComputeZones_basic'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/02/15 07:33:15 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/google -v -run=TestAccGoogleComputeZones_basic -timeout 120m
=== RUN   TestAccGoogleComputeZones_basic
--- PASS: TestAccGoogleComputeZones_basic (3.05s)
PASS
ok  	github.com/hashicorp/terraform/builtin/providers/google	3.079s

[stack72]

1 small question but LGTM!

[stack72]

should this be done using fmt.Sprintf rather than concatenation? I am not sure which is the right way to do it TBH

[radeksimko]

Yeah, sure, why not... I will change it

[radeksimko]

@stack72 Updated

[stack72]

LGTM!

[ghost]

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