logs should not report error when container don't set logpath.

[yanxuean]

Or indicate the user that the we cann't output logs because the container don't set logpath.

root@ubuntu:/home/cloud/test# crictl logs 331
FATA[0000] Get log path of container failed
root@ubuntu:/home/cloud/test#
root@ubuntu:/home/cloud/test#
root@ubuntu:/home/cloud/test# crictl inspect 331
DEBU[0000] ContainerStatusRequest: &ContainerStatusRequest{ContainerId:331,}
DEBU[0000] ContainerStatusResponse: &ContainerStatusResponse{Status:&ContainerStatus{Id:3317b118e40044e2ea8981e08bcece969f3b6533c087daeef0aa3f1bb9d2570c,Metadata:&ContainerMetadata{Name:busybox2,Attempt:0,},State:CONTAINER_RUNNING,CreatedAt:1509674580490484539,StartedAt:1509674623756901309,FinishedAt:0,ExitCode:0,Image:&ImageSpec{Image:busybox,},ImageRef:docker.io/library/busybox@sha256:0b408ce12dfae8721f5640f16f90f6592cda42a5bbc0a4ee2b31ee18c1b8985a,Reason:,Message:,Labels:map[string]string{},Annotations:map[string]string{},Mounts:[],LogPath:,},}