test: stop building URL's with host/port and Sprintf

[stbenjam]

You cannot build host:port in a URL with a simple Sprintf due to IPv6,
otherwise you'll produce invalid URL's. This moves to using
net.JoinHostPort to build URL's instead.

[openshift-ci]

@stbenjam: The following tests failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
ci/prow/e2e-aws-disruptive	14a416c	link	/test e2e-aws-disruptive
ci/prow/e2e-aws-serial	14a416c	link	/test e2e-aws-serial
ci/prow/e2e-gcp-upgrade	14a416c	link	/test e2e-gcp-upgrade

Full PR test history. Your PR dashboard.

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[stbenjam]

We also need openshift/kubernetes#628

[smarterclayton]

/lgtm

[smarterclayton]

Looks like everything passed, clearing the queue.

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: smarterclayton, stbenjam

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