CentOS 8: Drop trickle install to build freezer

Trickle was previously installed from EPEL7, but is not available in
EPEL8. It does not appear critical to the functioning of freezer, so
drop it to allow freezer images to build for CentOS 8.

Change-Id: I3e12ab51e9f01d383268d75ce72903686564ada6
Partially-Implements: blueprint centos-rhel-8

docker/freezer/freezer-base/Dockerfile.j2

@@ -20,10 +20,12 @@ RUN echo '{{ install_type }} not yet available for {{ base_distro }}' \
     && /bin/false
 
 {% elif install_type == 'source' %}
-    {% set freezer_base_packages = [
-        'trickle'
-    ] %}
+    {% if distro_package_manager != 'dnf' %}
+        {% set freezer_base_packages = [
+            'trickle'
+        ] %}
 {{ macros.install_packages(freezer_base_packages | customizable("packages")) }}
+    {% endif %}
 
 ADD freezer-base-archive /freezer-base-source
 

kolla/image/build.py

@@ -154,7 +154,6 @@ UNBUILDABLE_IMAGES = {
 
     'centos8+source': {
         "cyborg-agent",          # opae-sdk does not support CentOS 8
-        "freezer-base",          # Missing package trickle
     },
 
     'debian': {

releasenotes/notes/freezer-drop-trickle-9b3eaaa7d1e4ea5a.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    The ``trickle`` package is no longer available for CentOS 8, and has been
+    removed from the CentOS 8 Freezer images.