task service: return known error type
task service: return known error type

Found this error in a docker daemon log classified as an "uknown" error.
Since we know what this is return the correct error type so it can be
handled.

Signed-off-by: Brian Goff <dc73d0991b982a8303e713ef531a313af77e242a@gmail.com>

mikebrow/containerd,containerd/containerd,mikebrow/containerd,dmcgowan/containerd,dmcgowan/containerd,estesp/containerd,estesp/containerd,containerd/containerd,thaJeztah/containerd,thaJeztah/containerd