CLOUDSTACK-6940:Templates cannot be downloaded from URLs without
matching file extensions.
CLOUDSTACK-6941: Can't choose storage for the volume, when attaching uploaded data volume to VM

Changes:
- Only way to choose a certain storage pool is by using disk_offering_tags
- Added a parameter to take in a disk offering Id.
- Admin will have to create a custom sized disk offering and tag it as necessary for the user
- This custom offering Id should be passed during uploadVolume to associate the volume with this disk offering
CLOUDSTACK-6636: [Windows] Can not create Template from ROOT snapshot on Windows management server with Xen/NFS storage type. This change is only for XenServer with NFS Storage Server. Will fix remaining when we touch them.

Signed-off-by: Koushik Das <koushik@apache.org>