Don't trigger udev if socket is not accessible
    
    In container environments or rpm-ostree systems, scriptlets are not
    directly run on a host system. Thus, there's no point in asking udev to
    reload and retrigger: the host udev wouldn't see the new rules anyway.
    
    Let's just generalize this by checking if the udev socket even exists.
    If not, then we can't talk to `udevd` and we should just skip the reload
    & trigger bits.
    
    Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1753786