Add openvz/lxc discovery

cdist/conf/explorer/machine_type

@@ -22,6 +22,17 @@
 
 # FIXME: other system types (not linux ...)
 
+if [ -d "/proc/vz" -a ! -d "/proc/bc" ]; then
+    echo openvz
+    exit
+fi
+
+if [ -e "/proc/1/environ" ] &&
+    cat "/proc/1/environ" | tr '\000' '\n' | grep -Eiq '^container='; then
+    echo lxc
+    exit
+fi
+
 if [ -r /proc/cpuinfo ]; then
     # this should only exist on virtual guest machines,
     # tested on vmware, xen, kvm