Use slave template namespace in logs

[MarkTickner]

This defaults to client namespace as before. Currently it logs the master namespace, even if the slaves are being provisioned elsewhere.

[oliverlockwood]

For a bit more context, example logs from this before the fix:

INFO: Total container cap of 5 reached, not provisioning: 5 running or errored in namespace jenkins-master with Kubernetes labels {jenkins=slave}

versus

INFO: Created Pod: jenkins-slave-uber-s75w0 in namespace jenkins-slaves

[carlossg]

Thanks!