Move Mount into mount pkg

This moves both the Mount type and mountinfo into a single mount
package.

This also opens up the root of the repo to hold the containerd client
implementation.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

mount/mountinfo_unsupported.go

@@ -0,0 +1,18 @@
+// +build !linux,!freebsd,!solaris freebsd,!cgo solaris,!cgo
+
+package mount
+
+import (
+	"fmt"
+	"runtime"
+)
+
+// Self retrieves a list of mounts for the current running process.
+func Self() ([]Info, error) {
+	return nil, fmt.Errorf("mountinfo.Self is not implemented on %s/%s", runtime.GOOS, runtime.GOARCH)
+}
+
+// PID collects the mounts for a specific process ID.
+func PID(pid int) ([]Info, error) {
+	return nil, fmt.Errorf("mountinfo.PID is not implemented on %s/%s", runtime.GOOS, runtime.GOARCH)
+}