Add resize node function for azure driver

[rajat-garg-del]

Feature Request

To start with we have def ex_change_node_size(self, node, new_size) function in [https://github.com/apache/libcloud/blob/trunk/libcloud/compute/drivers/ec2.py] which supports instance type change for AWS.

We need similar functionality for Azure cloud as well where we could change the vmSize for Azure cloud. This could be done by adding node_resize function at (https://github.com/apache/libcloud/blob/trunk/libcloud/compute/drivers/azure_arm.py )