Only replace python when re-initializing the venv

We reinitialize the venv to ensure that the right version of
python is in the venv, but we do not want virtualenv to also
replace pip, setuptools and wheel so we tell it not to. If we
don't do this then virtualenv will install the latest available
version, which is not what we want.

Change-Id: I5f7e8fd36185537543d0741d88a5ccc9cd1f1645
Partial-Bug: #1764470
(cherry picked from commit a686b93020)

tasks/nova_install.yml

@@ -156,11 +156,22 @@
     - ansible_pkg_mgr in ['yum', 'dnf', 'zypper']
     - nova_get_venv | changed
 
+# NOTE(odyssey4me):
+# We reinitialize the venv to ensure that the right
+# version of python is in the venv, but we do not
+# want virtualenv to also replace pip, setuptools
+# and wheel so we tell it not to.
+# We do not use --always-copy for CentOS/SuSE due
+# to https://github.com/pypa/virtualenv/issues/565
 - name: Update virtualenv path
   shell: |
     find {{ nova_bin }} -name \*.pyc -delete
     sed -si '1s/^.*python.*$/#!{{ nova_bin | replace ('/','\/') }}\/python/' {{ nova_bin }}/*
-    virtualenv {{ nova_bin | dirname }}
+    virtualenv {{ nova_bin | dirname }} \
+        {{ (ansible_pkg_mgr == 'apt') | ternary('--always-copy', '') }} \
+        --no-pip \
+        --no-setuptools \
+        --no-wheel
   when:
     - nova_get_venv | changed
   tags: