Cloudstack Driver - Create/Delete Network functionality + tests

Functions added on the cloudstack driver:
 
ex_list_network_offering
ex_create_network
ex_delete_network

New Object:
CloudStackNetworkOffering

And some additions to the CloudStackNetwork dictionary
netmask
gatway
vpcid
Yeah, and it's also worth noting that compute drivers should only implement user / non-admin functionality.

We need to find a better and unified solution (maybe a separate driver / class) for handling admin actions, but this requires a bit more thought and work.