refactoring tests, add Bossan::Test::TestCase.

Refactoring tests.
Add test endpoint script test/driver.rb.
Add useful test class Bossan::Test::TestCase,
it automatically starts/stops server when running tests.
fix Rakefile, restore pwd
modify bossan_test.rb to support ruby 2.0
add close(listen_sock) to bossan_run_loop
Merge pull request #13 from kubo39/refactor-test

Refactoring tests, add Bossan::Test::TestCase.