travis: remove known hosts, system_site_packages, cython
travis: remove known hosts, system_site_packages, cython

openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro