Add a new 'kernel' feature source, detecting the kernel version. The
kernel version is split into multiple labels in order to make this more
usable in label selectors. Kernel version in the format X.Y.Z-patch will
be presented as
node.alpha.kubernetes-incubator.io/nfd-kernel-version.full=X.Y.Z-patch
node.alpha.kubernetes-incubator.io/nfd-kernel-version.major=X
node.alpha.kubernetes-incubator.io/nfd-kernel-version.minor=Y
node.alpha.kubernetes-incubator.io/nfd-kernel-version.revision=Z
The '.full' label will always be avaiable. The other labels if these
components can be parsed from the kernel version number.
