MFC:
r295924: Make sure that hash-based db files fsync befor closing/syncing.
r295925: We no longer need O_SYNC pwd_mkd
r295465: We no longer need O_SYNC on services_mkdb
r295800: We no longer need O_SYNC on cap_mkdb

This should improve the performance of building db files.

MFC r285050, r285053, r285059:

When passwd or group information is changed (by pw, vipw, chpass, ...)
temporary file is created and then a rename() call move it to official file.
This operation didn't have any check to make sure data was written to disk
and if a power cycle happens system could end up with a 0 length passwd
or group database.

There is a pfSense bug with more information about it:

https://redmine.pfsense.org/issues/4523

The following changes were made to protect passwd and group operations:

* lib/libutil/gr_util.c:
- Replace mkstemp() by mkostemp() with O_SYNC flag to create temp file
- After rename(), fsync() call on directory for faster result

* lib/libutil/pw_util.c
- Replace mkstemp() by mkostemp() with O_SYNC flag to create temp file

* usr.sbin/pwd_mkdb/pwd_mkdb.c
- Added O_SYNC flag on dbopen() calls
- After rename(), fsync() call on directory for faster result

* lib/libutil/pw_util.3
- pw_lock() returns a file descriptor to master password file on success

Differential Revision: https://reviews.freebsd.org/D2978
Approved by: re (kib), bapt (implicit agreed)
Sponsored by: Netgate

MFC r285050, r285053, r285059:

When passwd or group information is changed (by pw, vipw, chpass, ...)
temporary file is created and then a rename() call move it to official file.
This operation didn't have any check to make sure data was written to disk
and if a power cycle happens system could end up with a 0 length passwd
or group database.

There is a pfSense bug with more information about it:

https://redmine.pfsense.org/issues/4523

The following changes were made to protect passwd and group operations:

* lib/libutil/gr_util.c:
- Replace mkstemp() by mkostemp() with O_SYNC flag to create temp file
- After rename(), fsync() call on directory for faster result

* lib/libutil/pw_util.c
- Replace mkstemp() by mkostemp() with O_SYNC flag to create temp file

* usr.sbin/pwd_mkdb/pwd_mkdb.c
- Added O_SYNC flag on dbopen() calls
- After rename(), fsync() call on directory for faster result

* lib/libutil/pw_util.3
- pw_lock() returns a file descriptor to master password file on success

Differential Revision: https://reviews.freebsd.org/D2978
Approved by: re (kib), bapt (implicit agreed)
Sponsored by: Netgate