Update containerd to ec15fe95aa.

Signed-off-by: Lantao Liu <lantaol@google.com>

vendor/github.com/Microsoft/hcsshim/cgo.go

@@ -0,0 +1,7 @@
+package hcsshim
+
+import "C"
+
+// This import is needed to make the library compile as CGO because HCSSHIM
+// only works with CGO due to callbacks from HCS comming back from a C thread
+// which is not supported without CGO. See https://github.com/golang/go/issues/10973