Fix get-pip for python 3.5

get-pip.py is fixed for py2.7 in
https://review.opendev.org/c/openstack/devstack/+/772462

This commit support it for py3.5 as devstack stable/train and stein
still support ubuntu xenial which has py3.5

Also using Temepst 23.0.0 for xenial platform job which is
compatible version on py3.5.

Closes-Bug: #1913283
Change-Id: Icd40e41b5f3ef9a621ca1b9739875fcdd31abd74

.zuul.yaml

@@ -541,6 +541,10 @@
     parent: tempest-full
     description: Ubuntu Xenial platform test
     nodeset: openstack-single-node-xenial
+    vars:
+      devstack_localrc:
+        # use py3.5 compatible Tempest here.
+        TEMPEST_BRANCH: "23.0.0"
     voting: false
 
 - job:

tools/install_pip.sh

@@ -102,6 +102,10 @@ function _install_get_pip {
 function install_get_pip {
     _install_get_pip python $PIP_GET_PIP_PY27_URL $LOCAL_PIP_PY27
     if python3_enabled; then
+        if [[ "$PYTHON3_VERSION" == "3.5" ]]; then
+            PIP_GET_PIP_URL=$(dirname $PIP_GET_PIP_URL)/3.5/$(basename $PIP_GET_PIP_URL)
+            LOCAL_PIP=${LOCAL_PIP}-py35
+        fi
         _install_get_pip python${PYTHON3_VERSION} $PIP_GET_PIP_URL $LOCAL_PIP
     fi
 }