Consistently use <lxc/lxccontainer.h> for the API

Consistently use <lxc/lxccontainer.h> for the API

The API header was included in a variety of ways before, standardize
those to "include <lxc/lxccontainer.h>" as this will always work both in
tree and on a system with the headers installed.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>