New --owner and --group for when they can't be read from the system

[mohammad-akhlaghi]

With these new options, its now possible to use metastore when getpwuid' and getgrgid' don't work (for example on a server when the user list isn't present in `/etc/passwd' directly, but hidden somewhere on the network. This problem actually occurred occured for me while trying to use metastore on a server and didn't allow me to use it. So it would probably be very useful for other users in such scenarios also.

I just haven't added the man-page entry for these options because I don't have any experience in them. If you feel its good to merge with master, could you please add man page entries for it too?