Add location to operation model
Add location to operation model

This commit aims to fix a warning when using the operation model api on a
recent LXD version.
https://github.com/lxc/lxd/commit/55fcda838f549203d4cd52d19eb9166b0ed31945
introduced the `location` field to the operations model.

Signed-off-by: David Negreira <fcf78d2bd18016ad1a0ae658a2dc23a39100147f@canonical.com>

lxc/pylxd,lxc/pylxd