kubeadm: Refactor InitConfiguration init APIs

Currently ConfigFileAndDefaultsToInternalConfig and
FetchConfigFromFileOrCluster are used to default and load InitConfiguration
from file or cluster. These two APIs do a couple of completely separate things
depending on how they were invoked. In the case of

ConfigFileAndDefaultsToInternalConfig, an InitConfiguration could be either
defaulted with external override parameters, or loaded from file.
With FetchConfigFromFileOrCluster an InitConfiguration is either loaded from
file or from the config map in the cluster.

The two share both some functionality, but not enough code. They are also quite
difficult to use and sometimes even error prone.

To solve the issues, the following steps were taken:

- Introduce DefaultedInitConfiguration which returns defaulted version agnostic
  InitConfiguration. The function takes InitConfiguration for overriding the
  defaults.

- Introduce LoadInitConfigurationFromFile, which loads, converts, validates and
  defaults an InitConfiguration from file.

- Introduce FetchInitConfigurationFromCluster that fetches InitConfiguration
  from the config map.

- Reduce, when possible, the usage of ConfigFileAndDefaultsToInternalConfig by
  replacing it with DefaultedInitConfiguration or LoadInitConfigurationFromFile
  invocations.

- Replace all usages of FetchConfigFromFileOrCluster with calls to
  LoadInitConfigurationFromFile or FetchInitConfigurationFromCluster.

- Delete FetchConfigFromFileOrCluster as it's no longer used.

- Rename ConfigFileAndDefaultsToInternalConfig to
  LoadOrDefaultInitConfiguration in order to better describe what the function
  is actually doing.

Signed-off-by: Rostislav M. Georgiev <rostislavg@vmware.com>

cmd/kubeadm/app/phases/addons/proxy/proxy_test.go

@@ -201,7 +201,7 @@ func TestEnsureProxyAddon(t *testing.T) {
 			masterConfig.Networking.PodSubnet = "2001:101::/96"
 		}
 
-		intMaster, err := configutil.ConfigFileAndDefaultsToInternalConfig("", masterConfig)
+		intMaster, err := configutil.DefaultedInitConfiguration(masterConfig)
 		if err != nil {
 			t.Errorf("test failed to convert external to internal version")
 			break

cmd/kubeadm/app/phases/uploadconfig/uploadconfig_test.go

@@ -84,7 +84,7 @@ func TestUploadConfiguration(t *testing.T) {
 					CRISocket: "/var/run/custom-cri.sock",
 				},
 			}
-			cfg, err := configutil.ConfigFileAndDefaultsToInternalConfig("", initialcfg)
+			cfg, err := configutil.DefaultedInitConfiguration(initialcfg)
 
 			// cleans up component config to make cfg and decodedcfg comparable (now component config are not stored anymore in kubeadm-config config map)
 			cfg.ComponentConfigs = kubeadmapi.ComponentConfigs{}