[cdc_stream] Add integration tests (#44)

This CL adds Python integration tests for cdc_stream. To run the
tests, you need to supply a Linux host and proper configuration for
cdc_stream to work:

set CDC_SSH_COMMAND=C:\path\to\ssh.exe <args>
set CDC_SCP_COMMAND=C:\path\to\scp.exe <args>
C:\python38\python.exe -m integration_tests.cdc_stream.all_tests --binary_path=C:\full\path\to\cdc_stream.exe --user_host=user@host

Ran the tests and made sure they worked.

integration_tests/cdc_stream/__init__.py

@@ -0,0 +1 @@
+