[cdc_rsync] Add integration tests (#42)

[cdc_rsync] Add integration tests

This CL adds Python integration tests for cdc_rsync. To run the tests,
you need to supply a Linux host and proper configuration for cdc_rsync
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_rsync.all_tests --binary_path=C:\full\path\to\cdc_rsync.exe --user_host=user@host

Ran the tests and made sure they worked.

integration_tests/__init__.py

@@ -0,0 +1,13 @@
+# Copyright 2022 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.