High: Filesystem: Add force_unmount option

This new option doesn't change any default behavior.

We need a safe way to kill processes accessing a mount point without relying on tools like lsof or fuser. Those tools cause problems with nfs mounts are in use on a system.  They perform operations that will block in a nfs mount is unresponsive. This causes filesystem resources completely unrelated to the unresponsive nfs mount to timeout.

With the 'force_unmount' option we can swtich between a purely shell method of scanning the procs directory for pids accessing the mount_point, or the previous default that uses 'fuser'.  We also have the new ability to disable killing the pids all together if we want by setting this option to 'false'