vfs_preopen: add useful debug messages which can be configured on adjustable log...

vfs_preopen: add useful debug messages which can be configured on adjustable log levels

The following are the default values:

  preopen:nomatch_log_level = 5
  preopen:match_log_level = 5
  preopen:nodigits_log_level = 1
  preopen:founddigits_log_level = 3
  preopen:reset_log_level = 5
  preopen:push_log_level = 3
  preopen:queue_log_level = 10

This gives admins a way to debug/audit the preopen usage.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>