Added a getTenantInfo to Openstack Identity

This function will give administrative option to get the tenant Info for a specified
tenantId. If no tenantId is specified it will return the tenant info of
the tenant to whom the auth token used belongs. Corresponding tests were
also added.
Merge pull request #176 from cngupte123/adding_tenantInfo_to_openstack_identity

Added getTenantInfo function to Openstack Identity