Previous versions of LXC never compiled in gnutls support due to a bug in the
configure script. As other TLS implementations are not supported and the feature
was disabled in previous builds, disable it during configure.
See https://github.com/lxc/lxc/pull/1360 for details regarding the bug in the
autoconf of the previous versions.
Signed-off-by: Karl Vogel <karl.vogel@gmail.com>