MFC r230296:

Don't write /var/db/zoneinfo when zone is not actually changed.

If the specified zone file does not exist or the -n flag is specified,
do not update /var/db/zoneinfo.

PR:		bin/164039
Submitted by:	dteske
MFC r230520:

Clean up reinstall option and remove duplicate code

- Move the reinstall logic to be before menus are initialised
  (menus are not needed when reinstalling a zonefile).

- Remove unnecessary re-initialization of path_db.

- Update variable name and error message because we now use the
  zone name relative to /usr/share/zoneinfo, not the full path.

PR:		bin/164041
Submitted by:	dteske