SYSDB: Return EOK in case a non-fatal issue happened
    
    There may be the case where we aren't able to merge the timestamps from
    the fast ts db, which are treated as non-fatal issues. In case it
    happens, let's return EOK instead of propagating the non-fatal error.
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>