Switch image for travis ci to xenial (#3340)
Switch image for travis ci to xenial (#3340)

trusty is too old to use it now.
kubernetes/dashboard,zreigz/dashboard,kubernetes/dashboard,zreigz/dashboard,floreks/dashboard,floreks/dashboard,kubernetes/dashboard,floreks/dashboard,floreks/dashboard,kubernetes/dashboard,floreks/dashboard,zreigz/dashboard,kubernetes/dashboard,zreigz/dashboard