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: Ie968a6ab5f37ed11a5d1b63c09fbdecfc8c33cc1
Partial-Bug: #1764470
(cherry picked from commit 17e57e14a8)

tasks/heat_install.yml

@@ -108,11 +108,22 @@
     - ansible_pkg_mgr in ['yum', 'dnf', 'zypper']
     - heat_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 {{ heat_bin }} -name \*.pyc -delete
     sed -si '1s/^.*python.*$/#!{{ heat_bin | replace ('/','\/') }}\/python/' {{ heat_bin }}/*
-    virtualenv {{ heat_bin | dirname }}
+    virtualenv {{ heat_bin | dirname }} \
+        {{ (ansible_pkg_mgr == 'apt') | ternary('--always-copy', '') }} \
+        --no-pip \
+        --no-setuptools \
+        --no-wheel
   when: heat_get_venv | changed
   tags:
     - skip_ansible_lint