srand($seed) at the beginning of each test

To avoid `srand(0)` effect in the other tests, call `srand($seed)`
at the beginning of each test (setup).
[Feature #16655]

tool/lib/minitest/unit.rb

@@ -1297,6 +1297,8 @@ module MiniTest
         start_time = Time.now
 
         result = ""
+        srand(runner.options[:seed])
+
         begin
           @passed = nil
           self.before_setup

tool/test/minitest/metametameta.rb

@@ -47,6 +47,7 @@ class MetaMetaMetaTestCase < MiniTest::Unit::TestCase
     srand 42
     MiniTest::Unit::TestCase.reset
     @tu = MiniTest::Unit.new
+    @tu.options[:seed] = 42
 
     MiniTest::Unit.runner = nil # protect the outer runner from the inner tests
   end