Fix kubelet cadvisor stats runtime panic
Fixing a kubelet runtime panic when the runtime returns incomplete data:
```
E0729 08:17:47.260393 5218 panic.go:115] "Observed a panic" panic="runtime error: index out of range [0] with length 0" panicGoValue="runtime.boundsError{x:0, y:0, signed:true, code:0x0}" stacktrace=<
goroutine 174 [running]:
k8s.io/apimachinery/pkg/util/runtime.logPanic({0x33631e8, 0x4ddf5c0}, {0x2c9bfe0, 0xc000a563f0})
k8s.io/apimachinery/pkg/util/runtime/runtime.go:107 +0xbc
k8s.io/apimachinery/pkg/util/runtime.handleCrash({0x33631e8, 0x4ddf5c0}, {0x2c9bfe0, 0xc000a563f0}, {0x4ddf5c0, 0x0, 0x10000000043c9e5?})
k8s.io/apimachinery/pkg/util/runtime/runtime.go:82 +0x5e
k8s.io/apimachinery/pkg/util/runtime.HandleCrash({0x0, 0x0, 0xc000ae08c0?})
k8s.io/apimachinery/pkg/util/runtime/runtime.go:59 +0x108
panic({0x2c9bfe0?, 0xc000a563f0?})
runtime/panic.go:785 +0x132
k8s.io/kubernetes/pkg/kubelet/stats.(*cadvisorStatsProvider).ImageFsStats(0xc000535d10, {0x3363348, 0xc000afa330})
k8s.io/kubernetes/pkg/kubelet/stats/cadvisor_stats_provider.go:277 +0xaba
k8s.io/kubernetes/pkg/kubelet/images.(*realImageGCManager).GarbageCollect(0xc000a3c820, {0x33631e8?, 0x4ddf5c0?}, {0x0?, 0x0?, 0x4dbca20?})
k8s.io/kubernetes/pkg/kubelet/images/image_gc_manager.go:354 +0x1d3
k8s.io/kubernetes/pkg/kubelet.(*Kubelet).StartGarbageCollection.func2()
k8s.io/kubernetes/pkg/kubelet/kubelet.go:1472 +0x58
k8s.io/apimachinery/pkg/util/wait.BackoffUntil.func1(0x30?)
k8s.io/apimachinery/pkg/util/wait/backoff.go:226 +0x33
k8s.io/apimachinery/pkg/util/wait.BackoffUntil(0xc000add110, {0x3330380, 0xc000afa300}, 0x1, 0xc0000ac150)
k8s.io/apimachinery/pkg/util/wait/backoff.go:227 +0xaf
k8s.io/apimachinery/pkg/util/wait.JitterUntil(0xc000add110, 0x45d964b800, 0x0, 0x1, 0xc0000ac150)
k8s.io/apimachinery/pkg/util/wait/backoff.go:204 +0x7f
k8s.io/apimachinery/pkg/util/wait.Until(...)
k8s.io/apimachinery/pkg/util/wait/backoff.go:161
created by k8s.io/kubernetes/pkg/kubelet.(*Kubelet).StartGarbageCollection in goroutine 1
k8s.io/kubernetes/pkg/kubelet/kubelet.go:1470 +0x247
```
This commit fixes panics if:
- `len(imageStats.ImageFilesystems) == 0`
- `len(imageStats.ContainerFilesystems) == 0`
- `imageStats.ImageFilesystems[0].FsId == nil`
- `imageStats.ContainerFilesystems[0].FsId == nil`
- `imageStats.ImageFilesystems[0].UsedBytes == nil`
- `imageStats.ContainerFilesystems[0].UsedBytes == nil`
It also fixes the wrapped `nil` error for the check: `err != nil ||
imageStats == nil` in case that `imageStats == nil`.
Signed-off-by: Sascha Grunert <sgrunert@redhat.com>
50e430b3e9