Clean up second Gitaly process in tests

In tests, we spin up a separate Gitaly process for the second shard.  We
need to kill this process too to avoid leaking processes.

spec/support/helpers/test_env.rb

@@ -203,10 +203,13 @@ module TestEnv
     end
 
     gitaly_pid = Integer(File.read(TMP_TEST_PATH.join('gitaly.pid')))
+    gitaly2_pid = Integer(File.read(TMP_TEST_PATH.join('gitaly2.pid')))
     praefect_pid = Integer(File.read(TMP_TEST_PATH.join('praefect.pid')))
 
-    Kernel.at_exit { stop(gitaly_pid) }
-    Kernel.at_exit { stop(praefect_pid) }
+    Kernel.at_exit do
+      pids = [gitaly_pid, gitaly2_pid, praefect_pid]
+      pids.each { |pid| stop(pid) }
+    end
 
     wait('gitaly')
     wait('praefect')