LU-10918 pcc: auto RO-PCC caching when O_RDONLY open files

LU-10918 pcc: auto RO-PCC caching when O_RDONLY open files

During the file open() operation, if the file is being opened with
O_RDONLY flags, and the file matches the predefined rule, it will
be prefetched and attached into RO-PCC automatically.

Test-Parameters: clientcount=3 testlist=sanity-pcc,sanity-pcc,sanity-pcc
Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: Ib2c2ab51d67aed84eb7676c8df191faa33dfad39
Reviewed-on: https://review.whamcloud.com/41918
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>