LU-8900 snapshot: rename filesysetem fsname

LU-8900 snapshot: rename filesysetem fsname

Introuduce new tunefs options "--rename" for renaming the existing
Lustre filesystem fsname with configuration/parameters preserved.
Usage: tunefs.lustre --fsname $NEW_FSNAME --rename $OLD_FSNAME ...

NEW_FSNAME is the new fsname, must be specified.
OLD_FSNAME is the old fsname, it is optional if the MGS and the MDT
are combined together.

It shares the functionality of fork/erase Lustre configuration logs
in kernel.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Ic9aaf6ed6209c7580bfabd4b660a6a7667576484
Reviewed-on: https://review.whamcloud.com/24268
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Tested-by: Oleg Drokin <oleg.drokin@intel.com>