LU-13921 utils: new output format for ofd_access_log_reader

prefix every field with a tag to make it extensible:
o=l-OST0000 f=[0x1:0x1:0x0] t=1598363594 b=0 e=4096 s=4096 s=1 n=1 r=w

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Iab7d02852a1eb43d2259a4e914bafe87332749a6
Reviewed-on: https://review.whamcloud.com/39728
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Gu Zheng <gzheng@ddn.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>