infra-package-needs: install latest pip

The pip installed in the venv with "python3 -m venv" on Xenial is 8.X
-- this does not understand python_requires metadata on packages and
can thus pull in requirements that won't actually run inside the
virtualenv.

Avoid this by upgrading pip in the venv before installing.

While this is the immediate need; do the same on the other venv's we
create for general sanity.

Change-Id: I316e9587b6e290cd421b47f506c91dbebe0975c0

nodepool/elements/infra-package-needs/install.d/40-install-bindep

@@ -23,4 +23,11 @@ fi
 set -e
 
 python3 -m venv /usr/bindep-env
+if [[ ${DIB_RELEASE} == 'xenial' ]]; then
+    # The pip on xenial can't figure out it shouldn't install
+    # the latest pip; this is the last to support 3.5
+    /usr/bindep-env/bin/pip install --upgrade pip==20.3.4
+else
+    /usr/bindep-env/bin/pip install --upgrade pip
+fi
 /usr/bindep-env/bin/pip install bindep

nodepool/elements/infra-package-needs/install.d/40-install-tox

@@ -23,4 +23,11 @@ fi
 set -e
 
 python3 -m venv /usr/tox-env
+if [[ ${DIB_RELEASE} == 'xenial' ]]; then
+    # The pip on xenial can't figure out it shouldn't install
+    # the latest pip; this is the last to support 3.5
+    /usr/bindep-env/bin/pip install --upgrade pip==20.3.4
+else
+    /usr/bindep-env/bin/pip install --upgrade pip
+fi
 /usr/tox-env/bin/pip install tox

nodepool/elements/nodepool-base/install.d/91-venv-os-testr

@@ -19,4 +19,11 @@ fi
 set -e
 
 python3 -m venv /usr/os-testr-env
+if [[ ${DIB_RELEASE} == 'xenial' ]]; then
+    # The pip on xenial can't figure out it shouldn't install
+    # the latest pip; this is the last to support 3.5
+    /usr/bindep-env/bin/pip install --upgrade pip==20.3.4
+else
+    /usr/bindep-env/bin/pip install --upgrade pip
+fi
 /usr/os-testr-env/bin/pip install os-testr