Fix missing libcontainer syscall file

I noticed this file showed up when revendoring dependencies
with vndr.

Also removed `github.com/Microsoft/opengcs` from vendor.conf
as it was not used;

    2017/12/05 22:41:58 WARNING: package github.com/Microsoft/opengcs is unused, consider removing it from vendor.conf

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/github.com/opencontainers/runc/libcontainer/system/syscall_linux_32.go

@@ -0,0 +1,26 @@
+// +build linux
+// +build 386 arm
+
+package system
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+// Setuid sets the uid of the calling thread to the specified uid.
+func Setuid(uid int) (err error) {
+	_, _, e1 := unix.RawSyscall(unix.SYS_SETUID32, uintptr(uid), 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
+// Setgid sets the gid of the calling thread to the specified gid.
+func Setgid(gid int) (err error) {
+	_, _, e1 := unix.RawSyscall(unix.SYS_SETGID32, uintptr(gid), 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}