Update test/mochiweb_tests.erl

* With Erlang R16B03 running on FreeBSD/amd64 10.0-PRERELEASE
  (base/stable/10 r260159),
  the following tests will not finish
  within the default eunit timeout of 5 seconds
  (See `lib/eunit/src/eunit_internal.hrl` (of R16B03))
  so cases modified to extend timeout to 60 seconds (`LARGE_TIMEOUT`):

        % note well the underscore at the end of function names
        single_100k_http_POST_test_()
        single_100k_https_POST_test_()
        multiple_100k_http_POST_test_()
        multiple_100k_https_POST_test_()

  See also <https://github.com/mochi/mochiweb/commit/02066a511adcad08bb05d7a4a36ca1fc9ca08805>