Disable systemd in static build

This fix tries to address the warnings caused by static build
with go 1.9. As systemd needs dlopen/dlclose, the following warnings
will be generated for static build in go 1.9:
```
root@f4b077232050:/go/src/github.com/opencontainers/runc# make static
CGO_ENABLED=1 go build  -tags "seccomp cgo static_build" -ldflags "-w -extldflags -static -X main.gitCommit="1c81e2a794c6e26a4c650142ae8893c47f619764" -X main.version=1.0.0-rc4+dev " -o runc .
/tmp/go-link-113476657/000007.o: In function `_cgo_a5acef59ed3f_Cfunc_dlopen':
/tmp/go-build/github.com/opencontainers/runc/vendor/github.com/coreos/pkg/dlopen/_obj/cgo-gcc-prolog:76: warning: Using 'dlopen' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
```

This fix disables systemd when `static_build` flag is on (apply_nosystemd.go
is used instead).

This fix also fixes a small bug in `apply_nosystemd.go` for return value.

Signed-off-by: Yong Tang <[email protected]>

Author: yongtang

libcontainer/cgroups/systemd/apply_nosystemd.go

@@ -1,4 +1,4 @@
-// +build !linux
+// +build !linux static_build
 
 package systemd
 
@@ -43,7 +43,7 @@ func (m *Manager) GetStats() (*cgroups.Stats, error) {
 }
 
 func (m *Manager) Set(container *configs.Config) error {
-	return nil, fmt.Errorf("Systemd not supported")
+	return fmt.Errorf("Systemd not supported")
 }
 
 func (m *Manager) Freeze(state configs.FreezerState) error {

libcontainer/cgroups/systemd/apply_systemd.go

@@ -1,4 +1,4 @@
-// +build linux
+// +build linux,!static_build
 
 package systemd