snapd: drop valgrind from unit tests, fix static binary chceks
    
    Drop valgrind from build requires and unit tests, as it fails on ppc64el, see
    RHBZ#1766519.
    
    In rawhide, the static binary checks fails, fix it by making sure to redirect
    stderr.
    
    Signed-off-by: Maciek Borzecki <maciek.borzecki@gmail.com>