gh-45: add forgotten config file for test

test/box/snap_io_rate_limit.cfg

+# gh-45: snap_io_rate_limit was not taken into account if 
+# no other option has changed
+slab_alloc_arena = 0.1
+
+pid_file = "box.pid"
+
+logger="cat - >> tarantool.log"
+
+primary_port = 33013
+secondary_port = 33014
+admin_port = 33015
+
+rows_per_wal = 50
+too_long_threshold=2
+# 1MBps
+snap_io_rate_limit = 1
+io_collect_interval = 0.01
+