Move some disk operations from DomU to Dom0 to allow Nova
to run independently from the hypervisor.
Some disk types can be created in Dom0 (e.g. swap, ext3) but
others cannot. Add support here for creating those that can
in Dom0. This will be documented in the independent_compute
config flag in the last patch in this series.
Implements: blueprint xenapi-independent-nova
Change-Id: I634e783a5e19f9710544920e12300b299fc06b36
3e85b80649