prow: force namespace in deploy.sh

[spiffxp]

Related:

• apps/prow: Fix postsubmit failures. #2520 (comment) - in suggesting this change for another deploy script I realized we're not doing it for our build clusters
• hook up build clusters to prow staging instance #1475 - this change also adds service account and limit ranges for the k8s-infra-test-pods namespace to support k8s-infra-prow scheduling pods in k8s-infra-prow-build
• Setup a k8s-infra prow instance #1394

since resources are split into dir-per-namespace for our prow build
clusters, use the --namespace flag to make extra sure we don't
accidentally deploy a resource into a different namespace

[spiffxp]

/cc @ameukam

[dims]

/approve
/lgtm
/hold please remove hold when ready

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[spiffxp]

/hold cancel