Retry the sfdisk command up to 3 times.

Updates the nova baremetal-deploy-helper so that we retry
the fdisk command up to 3 times.

Previously the command would sometimes intermittently fail with
'Device or resource busy' errors. There doesn't seem to be a good way
to check/verify this other than to retry.

Fixes LP Bug #1191084.

Change-Id: I9c0733432dee5d556d6d2460db42f844e277c8de
Libvirt driver: normalize variable names (part1)

Variable names referring to the same objects/data are different
throughout the libvirt driver. This can lead to confusion, which
leads to avoidable bugs.

Part1:
    ctxt -> context
    instance_ref -> instance

Change-Id: I9d170b6025935544f07ecdebe5a68b2e2eaba5dd
Merge "Libvirt driver: normalize variable names (part1)"
Merge "Retry the sfdisk command up to 3 times."
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp