bug fix: setup disks to use cache=none to support live migration.

When executing a virsh live migration of a VM created by Kimchi, the
migration stops due to miss configuration "cache=none" on disk's
performance parameters.

Signed-off-by: Paulo Vital <pvital@linux.vnet.ibm.com>
Issue #333: do not encode error.html when the cherrpy version less than '3.2.5'

cherrypy does not encode the return of get_error_page from changeset 3591:35064e17ea5d.

The 3591:35064e17ea5d is lower than 3.2.5 version (changeset 3677:052f32b1d563).
And it is higher than 3.2.4 version (changeset 3497:cd8acbc5f2b3).

issue:
https://github.com/kimchi-project/kimchi/issues/333

Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>