Shell out instead of creating new JRuby runtimes in our integs

This avoids leaving extra runtimes around that just consume memory
during our integration tests, sometimes leading to OutOfMemory
situations.

integration-tests/spec/spec_helper.rb

@@ -138,13 +138,18 @@ def wildfly_server
 end
 
 def eval_in_new_ruby(script)
-  ruby = org.jruby.Ruby.new_instance
-  unless ENV['DEBUG']
-    dev_null = PLATFORM =~ /mswin/ ? 'NUL' : '/dev/null'
-    ruby.evalScriptlet("$stdout = File.open('#{dev_null}', 'w')")
+  tmpdir = Dir.mktmpdir("tmptorqueboxeval", ".")
+  script_path = "#{tmpdir}/script.rb"
+  begin
+    File.open(script_path, "w") { |f| f.write(script) }
+    command = %Q(#{jruby_command} #{jruby_jvm_opts} "#{script_path}" 2>&1)
+    output = `#{command}`
+    if ENV['DEBUG']
+      puts output
+    end
+  ensure
+    FileUtils.rm_rf(tmpdir)
   end
-  ruby.evalScriptlet(script)
-  ruby.tearDown(false)
 end
 
 ALREADY_BUNDLED = []