fix http_proxy warnings from grpc in tests

Example:
$ python setup.py nosetests --tests apache_beam.internal.http_client_test:HttpClientTest,apache_beam.runners.portability.fn_api_runner_test:FnApiRunnerSplitTest
/usr/local/google/home/ehudm/virtualenvs/beamenv/local/lib/python2.7/site-packages/setuptools/dist.py:475: UserWarning: Normalizing '2.13.0.dev' to '2.13.0.dev0'
normalized_version,
running nosetests
running egg_info
writing requirements to apache_beam.egg-info/requires.txt
writing apache_beam.egg-info/PKG-INFO
writing top-level names to apache_beam.egg-info/top_level.txt
writing dependency_links to apache_beam.egg-info/dependency_links.txt
writing entry points to apache_beam.egg-info/entry_points.txt
reading manifest file 'apache_beam.egg-info/SOURCES.txt'
reading manifest template 'MANIFEST.in'
warning: no files found matching 'README.md'
warning: no files found matching 'NOTICE'
warning: no files found matching 'LICENSE'
writing manifest file 'apache_beam.egg-info/SOURCES.txt'
test_get_new_http_proxy_info (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_get_new_http_timeout (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_proxy_from_env_http_with_port (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_proxy_from_env_http_without_method (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_proxy_from_env_http_without_port (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_proxy_from_env_http_without_port_without_method (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_proxy_from_env_https_with_port (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_proxy_from_env_https_without_method (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_proxy_from_env_https_without_port (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_proxy_from_env_https_without_port_without_method (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_proxy_from_env_invalid_var (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_proxy_from_env_wrong_method_in_url (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_proxy_from_env_wrong_method_in_var_name (apache_beam.internal.http_client_test.HttpClientTest) ... ok
test_checkpoint (apache_beam.runners.portability.fn_api_runner_test.FnApiRunnerSplitTest) ... E0409 15:40:15.297902625 9123 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:15.308364380 9161 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:15.310809798 9161 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
ok
test_checkpoint_sdf (apache_beam.runners.portability.fn_api_runner_test.FnApiRunnerSplitTest) ... E0409 15:40:15.749081921 9123 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:15.758503428 9190 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:15.763112931 9190 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
ok
test_nosplit_sdf (apache_beam.runners.portability.fn_api_runner_test.FnApiRunnerSplitTest) ... E0409 15:40:16.279301379 9123 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:16.289099978 9228 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:16.293335274 9228 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
ok
test_split_crazy_sdf (apache_beam.runners.portability.fn_api_runner_test.FnApiRunnerSplitTest) ... E0409 15:40:16.627109820 9123 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:16.636061947 9269 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:16.639386870 9269 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
ok
test_split_half (apache_beam.runners.portability.fn_api_runner_test.FnApiRunnerSplitTest) ... E0409 15:40:17.060748511 9123 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:17.069971138 9299 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:17.074126187 9299 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
ok
test_split_half_sdf (apache_beam.runners.portability.fn_api_runner_test.FnApiRunnerSplitTest) ... E0409 15:40:17.474129955 9123 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:17.483980537 9328 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
E0409 15:40:17.486675621 9328 http_proxy.cc:58] 'smtp' scheme not supported in proxy URI
ok

----------------------------------------------------------------------
XML: /usr/local/google/home/ehudm/src/beam/sdks/python/nosetests.xml
----------------------------------------------------------------------
Ran 19 tests in 2.603s

OK