locking: Add io_timeout to sanlock
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1251190
    
    So, if domain loses access to storage, sanlock tries to kill it
    after some timeout. So far, the default is 80 seconds. But for
    some scenarios this might not be enough. We should allow users to
    adjust the timeout according to their needs.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>