Merge pull request #620 from estesp/runinuserns-nonlinux

Stub RunningInUserNS for non-Linux

libcontainer/system/unsupported.go

@@ -0,0 +1,9 @@
+// +build !linux
+
+package system
+
+// RunningInUserNS is a stub for non-Linux systems
+// Always returns false
+func RunningInUserNS() bool {
+	return false
+}