Adding full AzureStack and custom cloud support and tests

Author: ryanschaaf-dmc

README.md

@@ -479,6 +479,34 @@ _Note: this option is **not valid** if you are planning to take Azure snapshots
 
     > Available values for `AZURE_CLOUD_NAME`: `AzurePublicCloud`, `AzureUSGovernmentCloud`, `AzureChinaCloud`
 
+
+### Using Azure Custom or Stack clouds
+
+When using custom Azure clouds, there are two methods to configure velero. 
+
+#### Option 1: Use Azure ResourceManager endpoint discovery
+
+  ```bash
+  cat << EOF > ./credentials-velero
+  AZURE_CLOUD_NAME=AzureCustomCloud
+  AZURE_METADATA_HOST=<Azure metadata host. For example, https://management.usgovcloudapi/net>
+  EOF
+  ```
+
+#### Option 2: Use Azure cloud configuration
+
+_Note: This is the best option when using AzureStackCloud_
+
+1. Ensure that a valid [cloud provider configuration](https://cloud-provider-azure.sigs.k8s.io/install/configs/) has been created. If using AKS, this can be mounted from the host path `/etc/kubernetes/azurestackcloud.json`
+2. Ensure that the environment variable `AZURE_ENVIRONMENT_FILEPATH` has been set to the location of the file from step 1
+3. Set the configuration (cloud name **must** be `AzureStackCloud`)
+
+  ```bash
+  cat << EOF > ./credentials-velero
+  AZURE_CLOUD_NAME=AzureStackCloud
+  EOF
+  ```
+
 ## Install and start Velero
 
 [Download][6] Velero

backupstoragelocation.md

@@ -72,4 +72,9 @@ spec:
     #
     # Optional (defaults to 1048576, i.e. 1MB, maximum 104857600, i.e. 100MB).
     blockSizeInBytes: "1048576"
+
+    # APIVersion to use with Azure client API calls for storage.
+    #
+    # Optional.
+    apiVersion: ""
 ```

velero-plugin-for-microsoft-azure/object_store.go

@@ -35,6 +35,7 @@ import (
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 
+	"github.com/vmware-tanzu/velero-plugin-for-microsoft-azure/velero-plugin-for-microsoft-azure/util"
 	veleroplugin "github.com/vmware-tanzu/velero/pkg/plugin/framework"
 	"github.com/vmware-tanzu/velero/pkg/util/azure"
 )
@@ -227,11 +228,12 @@ func (o *ObjectStore) Init(config map[string]string) error {
 		azure.BSLConfigUseAAD,
 		azure.BSLConfigStorageAccountAccessKeyName,
 		credentialsFileConfigKey,
+		util.ApiVersion,
 	); err != nil {
 		return err
 	}
 
-	client, cred, err := NewStorageClient(o.log, config)
+	client, cred, err := util.NewStorageClient(o.log, config)
 	if err != nil {
 		return err
 	}