flannel: add unit tests for config loading

backfill unit tests to add coverage for loadFlannelNetConf and
loadFlannelSubnetEnv

plugins/meta/flannel/flannel_suite_test.go

@@ -11,7 +11,7 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-package main_test
+package main
 
 import (
 	"encoding/json"