tests: fix flaky HTTPRoute creation

[pmalek]

Previous attempt in #13 failed to account for the fact that if first call to Create() fails like so:

    test_httproute.go:164: failed to deploy httproute: admission webhook "httproutes.validation.ingress-controller.konghq.com" denied the request: Unable to validate HTTPRoute schema: making HTTP request: Post "https://10-244-227-242.dataplane-admin-9900d552-f1b5-41f1-bf65-ac46c3b727f9-9hlfz6624j.2e004961-3189-40ae-b0c4-d9c476a6fe9c.svc:8444/schemas/routes/validate": dial tcp 10.244.227.242:8444: connect: connection refused

then the variable set as result will be overwritten with an empty value and all the subsequent invocations will also fail with the following message:

    test_httproute.go:164: failed to deploy httproute: HTTPRoute.gateway.networking.k8s.io "" is invalid: [metadata.name: Required value: name or generateName is required, <nil>: Invalid value: "null": some validation rules were not checked because the object was invalid; correct the existing errors to complete validation]

This PR should fix that issue by not reusing the same variable as an argument and return value.