Use the "zone" feature for LuaJIT profiling.

Snabb Switch now tells the profiler what "zone" of computation is
executing at any given time. The profiler is then able to report on
each zone separately, when given the -jp=z flag.

The zone name for an app can be given explicitly as the "zone" field
of the app (or its class). If no name is given then one is guessed
based on the module name of the app's code.

Example output:

    # ./snabbswitch -jp=2zF -t apps.intel.intel_app
    75%  apps.intel.intel_app
      -- 18%  intel10g.lua:transmit < intel_app.lua:push
      -- 17%  intel10g.lua:receive < intel_app.lua:pull
      -- 11%  buffer.lua:free < packet.lua:free
      --  7%  intel10g.lua:sync_transmit < intel_app.lua:push
      --  5%  intel10g.lua:can_add_receive_buffer < intel_app.lua:add_receive_buffers
      --  4%  register.lua:RDH < intel10g.lua:sync_receive
      --  3%  freelist.lua:add < buffer.lua:free
      --  3%  intel10g.lua:add_receive_buffer < intel_app.lua:add_receive_buffers
      --  3%  link.lua:receive < intel_app.lua:push
      --  3%  link.lua:transmit < intel_app.lua:pull
      --  3%  freelist.lua:remove < packet.lua:allocate
    11%  Sink
      -- 48%  buffer.lua:free < packet.lua:free
      -- 13%  freelist.lua:add < packet.lua:free
      -- 11%  link.lua:receive < basic_apps.lua:push
      --  9%  freelist.lua:add < buffer.lua:free
      --  7%  packet.lua:free < packet.lua:deref
      --  7%  packet.lua:deref < basic_apps.lua:push
    10%  Source
      -- 45%  packet.lua:add_iovec < basic_apps.lua:pull
      -- 15%  link.lua:transmit < basic_apps.lua:pull
      -- 15%  freelist.lua:remove < buffer.lua:allocate
      -- 11%  link.lua:full < link.lua:transmit
      --  8%  freelist.lua:remove < packet.lua:allocate
      --  6%  basic_apps.lua:pull < app.lua:breathe
     4%  selftest
      -- 27%  lib.lua:waitfor < register.lua:wait
      -- 27%  memory.lua:allocate_RAM < memory.lua:allocate_next_chunk
      -- 23%  app.lua:breathe < app.lua:main
      -- 14%  zone.lua:zone < app.lua:breathe
      --  5%  lib.lua:firstline < pci.lua:device_info
      --  5%  lib.lua:done < app.lua:main