Add DiffSuppressFunc to GKE cluster networks

[danawillow]

TestAccContainerCluster_network was failing with a perma-diff after #391 because GKE returns the network as a name only, but we allow users to set it to the URL. Add a DiffSuppressFunc to fix the test:

$ make testacc TEST=./google TESTARGS='-run=TestAccContainerCluster_network'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./google -v -run=TestAccContainerCluster_network -timeout 120m
=== RUN   TestAccContainerCluster_network
--- PASS: TestAccContainerCluster_network (348.82s)
PASS
ok  	github.com/terraform-providers/terraform-provider-google/google	348.976s

[rosbo]

You should use compareSelfLinkOrResourceName.

[rosbo]

Hum. This method assume that the API always return a self-link... It wouldn't work and updating linkDiffSuppress is dangerous because moving a resource to a different zone wouldn't trigger a diff like explained below.

You can either create a new method. Or when you store the network in the Read method, you can generate the relative part of the network and use compareSelfLinkOrResourceName.

[rosbo]

The problem with updating this method is that this will cause issue for zonal or regional self-link

If field was "regions/us-east1/someResource/myResource" and now is "regions/us-west1/someResource/myResource" this would suppress the diff.

I wouldn't update this method and use the other more robust compareSelfLinkOrResourceName

[danawillow]

All right, I solved it in a slightly different way from your suggestion (used a StateFunc instead), let me know what you think.

$ make testacc TEST=./google TESTARGS='-run=TestAccContainerCluster_network'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./google -v -run=TestAccContainerCluster_network -timeout 120m
=== RUN   TestAccContainerCluster_network
--- PASS: TestAccContainerCluster_network (402.15s)
PASS
ok  	github.com/terraform-providers/terraform-provider-google/google	402.316sv

(if you're happy with this feel free to merge instead of waiting for me since time zones / travel and whatnot)

[ghost]

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