Fix file descriptor leak when executing CA helpers
    
    cm_cadata_start_generic() creates a pipe. One half is passed
    to fetch(), the function that does all helper calls,
    via the cm_cadata_state variable ret. The other half is the
    reader and is used to detect execution errors. There is a pair
    of write/read on this descriptor which on error would be the
    errno.
    
    This second half wasn't being closed after reading to test for
    errors.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1992439
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>