Do not quite when pumactl unexpectedly exits.

When `pumactl` encounters issue, it exits [[1]]. That way also the whole
test suite unexpectedly exits. Rescuing `SystemExit` exception keeps the
test suite finish.

Fixes #2329

[1]: 0f718d516b/lib/puma/control_cli.rb (L272)

test/test_pumactl.rb

@@ -178,7 +178,10 @@ class TestPumaControlCli < TestConfigFileBase
   def assert_command_cli_output(options, expected_out)
     cmd = Puma::ControlCLI.new(options)
     out, _ = capture_subprocess_io do
-      cmd.run
+      begin
+        cmd.run
+      rescue SystemExit => e
+      end
     end
     assert_match expected_out, out
   end