FreeNAS Code

Make sure the nut daemons are dead. This closes a potential issue where nut stays up and running even after the service sliders claim things are off.

Don't reimport errno.

Fix a typo.

Simplify mntlock acquisition statements and simplify loops.

Fix the format string I added to volume_detach.

Rename volume_export to volume_detach to be more generic [1].
More 'renaming' needs to occur, but this will be an 8.2+ thing,
not an 8.0.3 thing (this is being done to avoid thrashing
dlavinge).

Mash zfs_export into volume_detach because it was only one
command.

Iterate through commands in a loop and stop at any errors to
ensure that things can be cleaned up at a later point in time
if something fails.

Document desired behavior and requirements.

1. Requested by jpaetzel.

try to catch MiddlewareError exceptions in django middleware instead of case by case

sysctl calls don't need to be printed out on the command line.

Fix some cornercases with adding users.

Here are the issues that pw doesn't catch that we care about:
- pw(8) doesn't restrict users from specifying regular files.
- pw(8) 'silently' fails (it complains via warn(3), but
doesn't return an exit code) if it can't create a home
directory (but only if the root path doesn't exist.. cute).
Example: pw doesn't create home directories if their base
directories don't exist, e.g. /mnt/tank/home/user where
/mnt/tank/home doesn't exist.

- Add a future hook for specifying the home directory mode,
as noted in ticket # 1117.

This doesn't fix modifying users, nor does it fix cleaning up
after users when deleted. This needs to be addressed in their
respective notifier APIs in future commits.

Tested with the following scenarios:

Sanity checks:
1. Create 'bar' with '/nonexistent'.
2. Create 'foo' with '/mnt/tank/foo'.
3. Create 'foo2' with '/mnt/tank/homes/foo', where
'/mnt/tank/homes' didn't already exist; this worked as
expected.

Negative tests:

1. Don't delete used directory:
a. Create 'foo' with '/mnt/tank/foo'.
b. mv /usr/sbin/pw /usr/sbin/pw.old .
c. Try to create 'foo2' with '/mnt/tank/foo'; this
failed but didn't nuke /mnt/tank/foo because it was
still in use.
2. Don't create user with a homedir pointing to a regular
file:
a. Try to create 'foo' with '/mnt/md_size'; failed as
expected.

Do not restart http here, it belongs elsewhere.

Do-Not-Merge: Don't put in TrueNAS