Update Azure SDK and support additional authentication schemes

Microsoft has updated the golang Azure SDK significantly.  Update the
azure storage driver to use the new SDK.  Add support for client
secret and MSI authentication schemes in addition to shared key
authentication.

Implement rootDirectory support for the azure storage driver to mirror
the S3 driver.

Signed-off-by: Kirat Singh <kirat.singh@beacon.io>

Co-authored-by: Cory Snider <corhere@gmail.com>

registry/storage/driver/azure/parser.go

@@ -0,0 +1,49 @@
+package azure
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/mitchellh/mapstructure"
+)
+
+const (
+	defaultRealm = "core.windows.net"
+)
+
+type Credentials struct {
+	Type     string `mapstructure:"type"`
+	ClientID string `mapstructure:"clientid"`
+	TenantID string `mapstructure:"tenantid"`
+	Secret   string `mapstructure:"secret"`
+}
+
+type Parameters struct {
+	Container        string      `mapstructure:"container"`
+	AccountName      string      `mapstructure:"accountname"`
+	AccountKey       string      `mapstructure:"accountkey"`
+	Credentials      Credentials `mapstructure:"credentials"`
+	ConnectionString string      `mapstructure:"connectionstring"`
+	Realm            string      `mapstructure:"realm"`
+	RootDirectory    string      `mapstructure:"rootdirectory"`
+	ServiceURL       string      `mapstructure:"serviceurl"`
+}
+
+func NewParameters(parameters map[string]interface{}) (*Parameters, error) {
+	params := Parameters{
+		Realm: defaultRealm,
+	}
+	if err := mapstructure.Decode(parameters, &params); err != nil {
+		return nil, err
+	}
+	if params.AccountName == "" {
+		return nil, errors.New("no accountname parameter provided")
+	}
+	if params.Container == "" {
+		return nil, errors.New("no container parameter provider")
+	}
+	if params.ServiceURL == "" {
+		params.ServiceURL = fmt.Sprintf("https://%s.blob.%s", params.AccountName, params.Realm)
+	}
+	return &params, nil
+}