buildroot

lxc: install also in staging

Install also lxc in staging directory, this will be needed for the
incoming integration of lxd package. Moreover, other packages could
find useful to integrate with liblxc instead of using lxc-xxx binaries.

Signed-off-by: Fabrice Fontaine <fabrice.fontaine@orange.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>