lxd/networks: Allow update/removal of node-specific key in non-clustered mode
lxd/networks: Allow update/removal of node-specific key in non-clustered mode

Updates doNetworkUpdate to detect when in non-clustered mode and allow the update/removal of node-specific keys when doing a PUT.

Otherwise it is not possible to update/remove node-specific keys when doing a PUT, as they are re-added from the current config.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

lxc/lxd,lxc/lxd,atxwebs/lxd,mjeanson/lxd,atxwebs/lxd,mjeanson/lxd,hallyn/lxd,hallyn/lxd,Skarlso/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd,hallyn/lxd,stgraber/lxd,Skarlso/lxd,stgraber/lxd,hallyn/lxd,Skarlso/lxd,stgraber/lxd,hallyn/lxd,Skarlso/lxd,stgraber/lxd,stgraber/lxd,mjeanson/lxd,atxwebs/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,atxwebs/lxd,lxc/lxd,lxc/lxd