client/lxd/storage/volumes: Fixes bug where migration errors were ignored
client/lxd/storage/volumes: Fixes bug where migration errors were ignored

This was a potentially serious bug as if you attempted to move a volume from one machine to another and the volume already existed on the remote side then even if it responded with an error, this error was ignored and the local volume was subsequently deleted without having copied it to the remote machine.

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

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