Fix the test-broker flags parsing

[mszostok]

This PR is a

• Feature Implementation
• Bug Fix
• Documentation

What this PR does / why we need it:

Right now when the test-broker will be executed then it always will throw the panic error:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x10c4a36]

goroutine 1 [running]:
flag.(*FlagSet).Parse(0x0, 0xc000010150, 0x3, 0x3, 0xc0000200b8, 0x0)
        /usr/local/go/src/flag/flag.go:922 +0x26
main.main()
        /go/src/github.com/kubernetes-incubator/service-catalog/contrib/cmd/test-broker/test-broker.go:52 +0x77
exit status 2

This PR is fixing that problem.

[k8s-ci-robot]

Hi @mszostok. Thanks for your PR.

I'm waiting for a kubernetes-incubator or kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[mszostok]

/kind bug

[jberkhahn]

/ok-to-test

[jberkhahn]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jberkhahn

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[jberkhahn]

/retest

[jberkhahn]

/test pull-service-catalog-xbuild

[jberkhahn]

/retest

[jberkhahn]

/test pull-service-catalog-xbuild