This gives the node e2e test binary a --feature-gates flag that populates a
FeatureGates field on the test context. The value of this field is forwarded
to the kubelet's --feature-gates flag and is also used to populate the global
DefaultFeatureGate object so that statically-linked components see the same
feature gate settings as provided via the flag.
This means that you can set feature gates via the TEST_ARGS environment
variable when running node e2e tests. For example:
TEST_ARGS='--feature-gates=DynamicKubeletConfig=true'
