Unify handling of --label-whitelist in nfd-worker and nfd-master. That is,
in nfd-worker, apply the regexp filter on non-namespaced part of the
label name.
Brief history:
1. Originally the whitelist regexp was applied on the full namespaced
label name (that would be e.g.
'feature.node.kubernetes.io/cpu-cpuid.AVX' in the current nfd version)
2. Commit 81752b2d changed the behavior so that the regexp was applied
on the non-namespaced part (that would be `cpu-cpuid.AVX`)
3. Commit 40918827 added support for custom label namespaces. With this
change, the label whitelist handling diverged between nfd-worker and
nfd-master. In nfd-master the whitelist regexp is always applied on
the non-namespaced label name. However, in nfd-worker the whitelist
handling is two-fold (and inconsistent): for labels in the standard
nfd namespace regexp is applied on the non-namespaced part (e.g.
`cpu-cpuid.AVX`, but, for labels in custom namespaces the regexp is
applied on the full name (e.g. `example.com/my-feature`).
This patch changes nfd-worker to behave similarly to nfd-master. The
namespace part is now always omitted, which should be easier for the
users to comprehend.
Also, fixes a bug in the label name prefixing so that the name of the
feature source is not prefixed into labels with custom label namespace
(effectively mangling the intended namespace). For example, previously a
'example.com/feature' label from the 'custom' feature source would be
prefixed with the source name, mangling it to
'custom-example.com/feature'.