fix compilation warning with malloc

src/lxc/lxc_execute.c

@@ -22,6 +22,7 @@
  */
 #define _GNU_SOURCE
 #include <stdio.h>
+#include <stdlib.h>
 #include <errno.h>
 #include <libgen.h>
 #include <string.h>

src/lxc/lxc_monitor.c

@@ -21,6 +21,7 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  */
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <libgen.h>
 #include <unistd.h>