Fixes: #14006Fixes: #14464
IPv6 wasn't supported for adding routes to the internet gateway.
Resulted in a message as follows:
```
Error creating route: MissingParameter: The request must contain the parameter destinationCidrBlock or destinationIpv6CidrBlock
```
```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSRoute_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/05/15 11:50:43 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSRoute_ -timeout 120m
=== RUN TestAccAWSRoute_basic
--- PASS: TestAccAWSRoute_basic (67.27s)
=== RUN TestAccAWSRoute_ipv6Support
--- PASS: TestAccAWSRoute_ipv6Support (59.35s)
=== RUN TestAccAWSRoute_ipv6ToInternetGateway
--- PASS: TestAccAWSRoute_ipv6ToInternetGateway (67.39s)
=== RUN TestAccAWSRoute_changeCidr
--- PASS: TestAccAWSRoute_changeCidr (103.68s)
=== RUN TestAccAWSRoute_noopdiff
--- PASS: TestAccAWSRoute_noopdiff (194.32s)
=== RUN TestAccAWSRoute_doesNotCrashWithVPCEndpoint
--- PASS: TestAccAWSRoute_doesNotCrashWithVPCEndpoint (71.36s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 563.397s
```
The "find route in table" helper code was not properly handling routes
with no destination CIDR block - like vpc_endpoint routes - so if one of
those routes would come up before the target route in the loop, we'd get
a crash.
Fixes#6337
Fixing basic acceptance test.
Adding warning to website about mixed mode.
Adding exists to aws_route.
Adding acceptance test for changing destination_cidr_block.
Paul Stack