rabbit_fifo_SUITE: Fix include of rabbit_fifo.hrl

We cannot use `-include_lib()` here because we are inside the
application.

It happened to work by chance because we use the Umbrella to work on all
projects, so rabbitmq-server is also inside `DEPS_DIR`. But when the
project is tested outside of the Umbrella, the testsuite failed to
compile.

Author: dumbbell

test/rabbit_fifo_SUITE.erl

@@ -11,8 +11,8 @@
 -include_lib("common_test/include/ct.hrl").
 -include_lib("eunit/include/eunit.hrl").
 -include_lib("ra/include/ra.hrl").
--include_lib("rabbit/src/rabbit_fifo.hrl").
 -include_lib("rabbit_common/include/rabbit.hrl").
+-include("src/rabbit_fifo.hrl").
 
 %%%===================================================================
 %%% Common Test callbacks