Don't require that the annotation value must conform to the (strict)
requirements of label values. In the Kubernetes API annotation values do
not have other restrictions than that the total size (keys and values)
of _all_ annotations combined of an object must not exceed 256kB.

This patch sets a maximum size limit of 1kB for the value of a single
feature annotation created by NFD. This limit is rather arbitrary but
should be enough for the NFD usage scenarios (until proven wrong).

Also add license header to the test.go file and fix one bug in
MatchFeature validation.