Fix ansible-test default image. (#31966)

* Add openssh-client to default docker container.
* Include Azure requirements in default container.

To do so, handling of pip requirements was updated to install each
set of requirements separately and then run a verification pass to
make sure there are no conflicts between requirements.

* Add missing --docker-no-pull option.
* Add documentation for the azure-requirements test.

test/runner/docker/requirements.sh

@@ -11,13 +11,60 @@ requirements=()
 
 for requirement in *.txt; do
     if [ "${requirement}" != "constraints.txt" ]; then
-        requirements+=("-r" "${requirement}")
+        requirements+=("${requirement}")
     fi
 done
 
 for python_version in "${python_versions[@]}"; do
+    version_requirements=()
+
+    for requirement in "${requirements[@]}"; do
+        case "${python_version}" in
+            "2.6")
+                case "${requirement}" in
+                    "integration.cloud.azure.txt") continue ;;
+                esac
+        esac
+
+        version_requirements+=("${requirement}")
+    done
+
+    echo "==> Installing pip for python ${python_version} ..."
+
     set -x
     "python${python_version}" /tmp/get-pip.py -c constraints.txt
-    "pip${python_version}" install --disable-pip-version-check -c constraints.txt "${requirements[@]}"
     set +x
+
+    echo "==> Installing requirements for python ${python_version} ..."
+
+    for requirement in "${version_requirements[@]}"; do
+        set -x
+        "pip${python_version}" install --disable-pip-version-check -c constraints.txt -r "${requirement}"
+        set +x
+    done
+
+    echo "==> Checking for requirements conflicts for ${python_version} ..."
+
+    after=$("pip${python_version}" list)
+
+    for requirement in "${version_requirements[@]}"; do
+        before="${after}"
+
+        set -x
+        "pip${python_version}" install --disable-pip-version-check -c constraints.txt -r "${requirement}"
+        set +x
+
+        after=$("pip${python_version}" list)
+
+        if [ "${before}" != "${after}" ]; then
+            echo "==> Conflicts detected in requirements for python ${python_version}: ${requirement}"
+            echo ">>> Before"
+            echo "${before}"
+            echo ">>> After"
+            echo "${after}"
+            exit 1
+        fi
+    done
+
+    echo "==> Finished with requirements for python ${python_version}."
 done