.travis, build: autodelete old unstable archives (#13867)

This commit adds a build step to travis to auto-delete unstable archives older than
14 days (our regular release schedule) from Azure via ci.go purge.

The commit also pulls in the latest Azure storage code, also switching over from
the old import path (github.com/Azure/azure-sdk-for-go) to the new split one
(github.com/Azure/azure-storage-go).

vendor/github.com/Azure/azure-storage-go/tableserviceclient.go

@@ -0,0 +1,20 @@
+package storage
+
+// TableServiceClient contains operations for Microsoft Azure Table Storage
+// Service.
+type TableServiceClient struct {
+	client Client
+	auth   authentication
+}
+
+// GetServiceProperties gets the properties of your storage account's table service.
+// See: https://docs.microsoft.com/en-us/rest/api/storageservices/fileservices/get-table-service-properties
+func (c *TableServiceClient) GetServiceProperties() (*ServiceProperties, error) {
+	return c.client.getServiceProperties(tableServiceName, c.auth)
+}
+
+// SetServiceProperties sets the properties of your storage account's table service.
+// See: https://docs.microsoft.com/en-us/rest/api/storageservices/fileservices/set-table-service-properties
+func (c *TableServiceClient) SetServiceProperties(props ServiceProperties) error {
+	return c.client.setServiceProperties(props, tableServiceName, c.auth)
+}