Add SANLOCK_RUN_DIR environment variable
    
    Using this environment variable, we can use custom run directory for
    placing sanlock socket and lockfile. This allows running sanlock as
    non-privileged user in the tests.
    
    When running the sanlock executable, we warn if using non-standard run
    directory, since this should be used only for testing.
    
    Signed-off-by: Nir Soffer <nsoffer@redhat.com>