Add file permission parameter to each file creation. fixes #138

Non daemonized fluentd, create a file as 0644 permission.
But daemonized fluentd, create a file as 0666 or other permission.
It is caused by File.umask(0) at daemonize process,
so we should specify file permission for better permission management.
Merge pull request #143 from fluent/daemonize-permission

Add file permission parameter to each file creation. fixes #138