[dvs] Update README with new flags, options, and known issues (sonic-…

…net#1380)

- Document --keeptb flag
- Add dynamic port option to ./create_vnet.sh
- Add libswsscommon installation issue

Signed-off-by: Danny Allen <daall@microsoft.com>

tests/README.md

@@ -54,7 +54,7 @@ For those developing new features for SWSS or the DVS framework, you might find
 
  ```
  docker run --privileged -id --name sw debian bash
- sudo ./create_vnet.sh sw
+ sudo ./create_vnet.sh -n 32 sw
  ```
 3. Start the DVS container:
 
@@ -97,16 +97,65 @@ For those developing new features for SWSS or the DVS framework, you might find
  sudo pytest --imgname=docker-sonic-vs:my-changes.333
  ```
 
+- You can also preserve a non-persistent DVS container for debugging purposes:
+
+ ```
+ sudo pytest --keeptb
+ ```
+
+ Which should give you something like this in `docker ps`:
+
+ ```
+ CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
+ 10bb406e7475 docker-sonic-vs:sonic-swss-build.1529 "/usr/bin/supervisord" 3 hours ago Up 3 hours ecstatic_swartz
+ edb35e9aa10b debian:jessie "bash" 3 hours ago Up 3 hours elegant_edison
+ ```
+
 - You can automatically retry failed test cases **once**:
 
  ```
  sudo pytest --force-flaky
  ```
 
 ## Known Issues
-- ```
- ERROR: Error response from daemon: client is newer than server (client API version: x.xx, server API version: x.xx)
+- You may encounter the test run being aborted before any cases are run:
  ```
+ daall@baker:~/sonic-swss/tests$ sudo pytest test_acl.py 
+ ============================= test session starts ==============================
+ platform linux -- Python 3.6.9, pytest-4.6.9, py-1.9.0, pluggy-0.13.1
+ rootdir: /home/daall/sonic-swss/tests
+ plugins: flaky-3.7.0
+ collected 25 items 
 
- You can mitigate this by editing the `DEFAULT_DOCKER_API_VERSION` in `/usr/local/lib/python2.7/dist-packages/docker/constants.py`, or by upgrading to a newer version of Docker CE. See [relevant GitHub discussion](https://github.com/drone/drone/issues/2048).
+ test_acl.py Aborted
+ ```
 
+ When run with the `-sv` flags we get some more information:
+ ```
+ daall@baker:~/sonic-swss/tests$ sudo pytest -sv test_acl.py 
+ ============================= test session starts ==============================
+ platform linux -- Python 3.6.9, pytest-4.6.9, py-1.9.0, pluggy-0.13.1 -- /usr/bin/python3
+ cachedir: .pytest_cache
+ rootdir: /home/daall/sonic-swss/tests
+ plugins: flaky-3.7.0
+ collected 25 items 
+
+ test_acl.py::TestAcl::test_AclTableCreation terminate called after throwing an instance of 'std::runtime_error'
+ what(): Sonic database config file doesn't exist at /var/run/redis/sonic-db/database_config.json
+ Aborted
+ ```
+
+ This indicates that something went wrong with the `libswsscommon` installation. The following should mitigate the issue:
+ ```
+ dpkg -r libswsscommon python3-swsscommon
+ dpkg --purge libswsscommon python3-swsscommon
+ rm -rf /usr/lib/python3/dist-packages/swsscommon/
+ dpkg -i libswsscommon.deb python3-swsscommon.deb
+ ```
+
+- You may encounter the following error message:
+ ```
+ ERROR: Error response from daemon: client is newer than server (client API version: x.xx, server API version: x.xx)
+ ```
+
+ You can mitigate this by upgrading to a newer version of Docker CE or editing the `DEFAULT_DOCKER_API_VERSION` in `/usr/local/lib/python3/dist-packages/docker/constants.py`, or by upgrading to a newer version of Docker CE. See [relevant GitHub discussion](https://github.com/drone/drone/issues/2048).