[17.12] daemon.cleanupContainer: nullify container RWLayer upon release

[thaJeztah]

back port of moby/moby#36160 and moby/moby#36242 for 17.12

git checkout -b 17.12-backport-layer-not-retained upstream/17.12
git cherry-pick -s -S -x -Xsubtree=components/engine e9b9e4ace294230c6b8eb010eda564a2541c4564
git cherry-pick -s -S -x -Xsubtree=components/engine 195893d38160c0893e326b8674e05ef6714aeaa4

Conflict in second commit due to moby/moby@87a1242 (moby/moby#35638) not being included in 17.12;

diff --cc components/engine/daemon/inspect.go
index 20cfa6ce2b,164e1aa2ae..0000000000
--- a/components/engine/daemon/inspect.go
+++ b/components/engine/daemon/inspect.go
@@@ -1,6 -1,7 +1,7 @@@
 -package daemon // import "github.com/docker/docker/daemon"
 +package daemon
  
  import (
+       "errors"
        "fmt"
        "time"
  
@@@ -187,10 -196,13 +195,18 @@@ func (daemon *Daemon) getInspectData(co
        // If container is marked as Dead, the container's graphdriver metadata
        // could have been removed, it will cause error if we try to get the metadata,
        // we can ignore the error if the container is dead.
++<<<<<<< HEAD
 +      if err != nil && !container.Dead {
 +              return nil, systemError{err}
++=======
+       if err != nil {
+               if !container.Dead {
+                       return nil, errdefs.System(err)
+               }
+       } else {
+               contJSONBase.GraphDriver.Data = graphDriverData
++>>>>>>> 195893d381... c.RWLayer: check for nil before use
        }
-       contJSONBase.GraphDriver.Data = graphDriverData
  
        return contJSONBase, nil
  }

ping @kolyshkin PTAL

[thaJeztah]

need to have a look at this

15:13:14 daemon/inspect.go:191:26: cannot convert "errors".New("RWLayer of container " + container.ID + " is unexpectedly nil") (type error) to type systemError: need type assertion
15:13:14 daemon/inspect.go:200:27: cannot convert err (type error) to type systemError: need type assertion

[kolyshkin]

From the first glance, systemError{err} (rather than systemError(err)) should be used. Here's the definition:

type systemError struct {
        cause error
}

[andrewhsu]

Closed in favour of #433