LU-16029 utils: add options to lr_reader to parse raw files

LU-16029 utils: add options to lr_reader to parse raw files

Add the following usages to lr_reader for post-mortem debuging:

debugfs -c -R "dump reply_data /tmp/reply_data" /dev/mapper/mds1
debugfs -c -R "dump last_rcvd /tmp/last_rcvd" /dev/mapper/mds1

lr_reader -cr -C /tmp/last_rcvd -R /tmp/reply_data
....

This patch attempts to re-refactoring lr_reader code.

It enable to use longer device name (by removing the limitation on
the 128 bytes buffer of debugfs command).

Signed-off-by: Etienne AUJAMES <etienne.aujames@cea.fr>
Change-Id: I6a5f945134d4235ac467ba2274eb05f71b468cd8
Reviewed-on: https://review.whamcloud.com/47988
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: DELBARY Gael <gael.delbary@cea.fr>
Reviewed-by: Oleg Drokin <green@whamcloud.com>