[ENHANCEMENT] Do we need stop -force|-f?

[yaazkal]

Is your feature request related to a problem? Please describe.
This is a follow up of PR #749

Describe the solution you'd like
As a fail unmount could happen for multiple reasons and can have side effects for the user, let's think if:

1. Also use the -f option of the umount system command if it's safe to do it in the stop command. Will this mean a new -f option to the stop command?

2. And what about to also giving an error_exit in the stop command if the unmount was not possible for any given reason? Also, will this mean a new -f option to the stop command?

3. destroy -f will use stop -f if gets implemented

cc @tschettervictor @bmac2 @cedwards

[tschettervictor]

@yaazkal I was wrong earlier. Using the -f option in destroy actually does a "zfs -rf destroy"

This means it attempts to force unmount the dataset when destroying it. But as we have seen this sometimes doesn't work, and can lead to data loss.

The only way in my experience past a failed unmount is a reboot of the server.

So I don't think having the -f option in stop.sh will help.