Specify a new interface for managing "raw" feature data. This is the
first step to separate raw feature data from node labels. None of the
feature sources implement this interface, yet.
This patch unifies the data format of "raw" features by dividing them
into three different basic types.
- keys, a set of names without any associated values, e.g. CPUID flags
or loaded kernel modules
- values, a map of key-value pairs, for features with a single value,
e.g. kernel config flags or os version
- instances, a list of instances each of which has multiple attributes
(key-value pairs of their own), e.g. PCI or USB devices
The new feature data types are defined in a new "pkg/api/feature"
package, catering decoupling and re-usability of code e.g. within future
extentions of the NFD gRPC API.
Rename the Discover() method of LabelSource interface to GetLabels().
Implement new registration infrastructure under the "source" package.
This change loosens the coupling between label sources and the
nfd-worker, making it easier to refactor and move the code around.
Also, create a separate interface (ConfigurableSource) for configurable
feature sources in order to eliminate boilerplate code.
Add safety checks to the sources that they actually implement the
interfaces they should.
In sake of consistency and predictability (of behavior) change all
methods of the sources to use pointer receivers.
Add simple unit tests for the new functionality and include source/...
into make test target.
