Move ContainerFlags to "commands" package

Commit 05513284e7 exposed the "rootfs"
and "no-pivot" flags for the "containers" command, but it accidentally
removed them for "run" since package-level variables are initialized
before package-level init functions in golang. Hoisting these flags to
a package imported by both commands solves the problem.

Signed-off-by: Felix Abecassis <fabecassis@nvidia.com>

cmd/ctr/commands/commands_unix.go

@@ -0,0 +1,33 @@
+// +build !windows
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package commands
+
+import (
+	"github.com/urfave/cli"
+)
+
+func init() {
+	ContainerFlags = append(ContainerFlags, cli.BoolFlag{
+		Name:  "rootfs",
+		Usage: "use custom rootfs that is not managed by containerd snapshotter",
+	}, cli.BoolFlag{
+		Name:  "no-pivot",
+		Usage: "disable use of pivot-root (linux only)",
+	})
+}