Validate log paths in sandbox and container config.
Validate log paths in sandbox and container config.

Only compose full container log path if neither of the paths is empty. Otherwise container won't start properly.

Signed-off-by: Cong Liu <847426650882ad95c8d64dd49005835e44b99713@google.com>

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