VMware VSphere SDK needs an up to date version of `pip` for the
installation step. With the current image, we face the following error:
```
(...)
02:27 Collecting git+https://github.com/vmware/vsphere-automation-sdk-python.git (from -r /root/ansible/test/lib/ansible_test/_data/requirements/integration.cloud.vcenter.txt (line 2))
02:27 Cloning https://github.com/vmware/vsphere-automation-sdk-python.git to /tmp/pip-req-build-pm27t16b
02:33 Requirement already satisfied: pyvmomi in /usr/local/lib/python3.6/dist-packages (from -r /root/ansible/test/lib/ansible_test/_data/requirements/integration.cloud.vcenter.txt (line 1)) (6.7.1.2018.12)
02:33 Requirement already satisfied: lxml>=4.3.0 in /usr/local/lib/python3.6/dist-packages (from vSphere-Automation-SDK==1.4.0->-r /root/ansible/test/lib/ansible_test/_data/requirements/integration.cloud.vcenter.txt (line 2)) (4.4.0)
02:33 Processing ./\\localhost/tmp/pip-req-build-pm27t16b/lib/vapi-runtime/vapi_runtime-2.12.0-py2.py3-none-any.whl
02:33 Could not install packages due to an EnvironmentError: [Errno 2] No such file or directory: '/root/ansible/\\\\localhost/tmp/pip-req-build-pm27t16b/lib/vapi-runtime/vapi_runtime-2.12.0-py2.py3-none-any.whl'
```
Bump default-test-container to 1.9.3 to get an up to date release of
`pip` (was 19.0.2, is now 19.2.3).
b68f5b406a