LU-13676 tools: awk script to find unique backtraces

LU-13676 tools: awk script to find unique backtraces

looking at backtraces from crash utility it's not routine to find
interesting ones. this simple awk script can help:

1) dump backtraces in crash using "foreach bt" command
2) cat <file-with-backtraces> | crash-find-unique-traces.awk

the output will be like:

schedule,schedule_timeout,osc_extent_wait,osc_cache_wait_range,
  osc_io_fsync_end,cl_io_end,lov_io_end_wrapper,lov_io_fsync_end,
  cl_io_end,cl_io_loop,cl_sync_file_range,ll_writepages,do_writepages,
  __writeback_single_inode,writeback_sb_inodes,wb_writeback,wb_workfn,
  process_one_work,worker_thread,kthread PIDs: 7
schedule,schedule_hrtimeout_range_clock,poll_schedule_timeout,
  do_sys_poll,__se_sys_poll PIDs: 2130
schedule,schedule_hrtimeout_range_clock,do_sigtimedwait,
  __se_sys_rt_sigtimedwait PIDs: 2251
schedule,osd_trans_stop,ofd_commitrw,tgt_brw_write,tgt_request_handle,
  ptlrpc_main,kthread PIDs: 11720
schedule,mdt_restriper_main PIDs: 12859
schedule,wb_wait_for_completion,sync_inodes_sb,sync_filesystem,
  generic_shutdown_super,kill_anon_super,deactivate_locked_super,
  cleanup_mnt,task_work_run,exit_to_usermode_loop PIDs: 15097

Test-Parameters: trivial
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I94514189f15cf559336217fddf7b665dde0c8f77
Reviewed-on: https://review.whamcloud.com/38936
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>