cleanup useless check in mirror test helper funcion 'CreateEmptyMirrors'

[Ks89]

Quick cleanup of mirror testhelper function as requested here https://github.com/k8snetworkplumbingwg/ovs-cni/pull/227#discussion_r979462642

If createEmptyMirror executed without an error, it's safe to assume that mirror is really in ovsdb Mirror table.

[kubevirt-bot]

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[phoracek]

/retest /lgtm /approve

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Ks89, phoracek

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[phoracek]

@Ks89 one of the mirror tests seems flakey, would you please look into it?

{ Failure /tmp/src/github.com/k8snetworkplumbingwg/ovs-cni/tests/mirror_test.go:86
Expected
    <string>: 09:02:10.934759 IP 10.0.0.1 > 10.0.0.2: ICMP echo request, id 8, seq 1, length 64

to contain substring
    <string>: IP 10.0.0.2 > 10.0.0.1: ICMP echo reply
/tmp/src/github.com/k8snetworkplumbingwg/ovs-cni/tests/mirror_test.go:102}

[Ks89]

We cannot reproduce this error in our environment, but it's probably related to a slower VM for kubevirtci. We tried to increase the timeout from 10s to 30s.

[phoracek]

/retest

[phoracek]

/lgtm

Thanks!

[phoracek]

/release-note-none