AppArmor: allow access to /sys/devices/system/node/node[0-9]*/meminfo.

abstractions/base allows access to /proc/meminfo already, so this doesn't leak
much more information. I can't be sure by looking at the code, but I would
not be surprised if Firefox needed more info about available memory
to manage it pool of content rendering processes, when e10s is enabled.

apparmor/torbrowser.Browser.firefox

@@ -77,6 +77,8 @@
 
   /sys/devices/system/cpu/ r,
   /sys/devices/system/cpu/present r,
+  /sys/devices/system/node/ r,
+  /sys/devices/system/node/node[0-9]*/meminfo r,
   deny /sys/devices/virtual/block/*/uevent r,
 
   # Should use abstractions/gstreamer instead once merged upstream