Stop relying on $HOSTNAME to identify the pod about networkservicemesh

[lixuna]

Points to note (@edwarnicke):

• we’d like the NSM to be as easy to use as possible,
• External network services may be a future use case

Problem (@fkautz):

• HOSTNAME is a settable variable in pod spec
• if HOSTNAME is not set, this approach may not work

Goal:

• to have a reference to match

Options:

• have an NSM agent on each node
• use pod name and namespace id
• run FS notifier, watch files for namespace

[fkautz]

There are currently three commands still relying on HOSTNAME:

• cmd/nsm-generate-sriov-configmap/nsm-generate-sriov-configmap.go
• cmd/nsm-init/nsm-init.go
• plugins/nsecommand/impl.go

[nickolaev]

The only remaining occurrence of this is in examples/cmd/nsm-generate-sriov-configmap/nsm-generate-sriov-configmap.go, which being an example is not that bad. Is this issue still valid?