Fix lockfile() to use the given "dir" argument
    
    lockfile() was using SANLK_RUN_DIR for creating the run directory, and
    the dir argument for building the lockfile path. Use only dir so we can
    create a lockfile in another directory. This will be useful for running
    sanlock as non-privileged user during the tests.
    
    Signed-off-by: Nir Soffer <nsoffer@redhat.com>