commit 2bf549084789d80eba807439da07cdaed024efb9
Author: Denis Zalevskiy <denis.zalevskiy@jolla.com>
Date:   Wed Mar 4 13:09:16 2015 +0200

    [hcb] do not use O_RDWR by default
    
    If file to store hcb is opened in O_RDWR mode just to be read and then closed,
    closing takes unacceptably long time if overlay is mounted on filesystems
    mounted in synchronous mode (tested it with dirsync,flush,discard, I guess this
    is effect from discard).
    
    Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
