Add HTTP-post check test

Add simple HTTP POST method test in test/test_rack_spec.rb
It checks only client-side, not checked ["rack.input"].
Some test files renamed

renamed 2 test files for humans.
* test/test_rack_env_simple_get.rb
* test/test_rack_env_simple_query.rb
Add some test case env for simple get

add some tests for server's env values for simple http get.
* env["SERVER_NAME"]
* env["SERVER_PORT"]
* env["HTTP_USER_AGENT"]
Add long url check test

add test to check long url query. if url size < 4096, returns HTTP Status code 200, or returns 400.