Improve RUBYOPT's handling in tests

When debugging the issue related to ruby/irb#919, I noticed that debugger tests don't respect the IRB version I specified in the Gemfile. This is because console tests force override the RUBYOPT env, which will remove the `-rbundler/setup` injected by bundler. Further more, if tests use `run_rdbg` with the `rubyopt` option, the RUBYOPT will be overridden yet again. So in this commit I did 2 improvements: 1. `run_rdbg` should append instead of override RUBYOPT 2. If tests are executed with bundler, we also run the debugger in PTY process with bundler by appending `-rbundler/setup` to RUBYOPT

Author: st0012

test/support/console_test_case.rb

@@ -225,7 +225,12 @@ def prepare_test_environment(program, test_steps, &block)
  @scenario = []
  test_steps.call
  @scenario.freeze
- inject_lib_to_load_path
+
+ ENV['RUBYOPT'] = "-I #{__dir__}/../../lib"
+
+ if ENV.key?('BUNDLE_GEMFILE')
+ ENV["RUBYOPT"] += " -rbundler/setup"
+ end
 
  block.call
 
@@ -283,7 +288,7 @@ def run_rdbg program, options: nil, rubyopt: nil, &test_steps
  prepare_test_environment(program, test_steps) do
  test_info = TestInfo.new(dup_scenario, 'LOCAL', /\(rdbg\)/)
  cmd = "#{RDBG_EXECUTABLE} #{options} -- #{temp_file_path}"
- cmd = "RUBYOPT=#{rubyopt} #{cmd}" if rubyopt
+ ENV["RUBYOPT"] += " #{rubyopt}" if rubyopt
  run_test_scenario cmd, test_info
  end
  end
@@ -301,10 +306,6 @@ def new_thread &block
  end
  end
 
- def inject_lib_to_load_path
- ENV['RUBYOPT'] = "-I #{__dir__}/../../lib"
- end
-
  def assert_empty_queue test_info, exception: nil
  message = "Expected all commands/assertions to be executed. Still have #{test_info.queue.length} left."
  if exception