lxc: disable lua and python

Also conditionally disable bash if bash isn't built. Fixes:
http://autobuild.buildroot.net/results/8ea/8ea1d682706ba5fee27a64008bb7237d53120e9b/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>