docs: Fix plugin registry generation failures

This patch set fixes plugin registry generation script which
is resulting in the documentation page ending up empty [0].

This is because the script `tools/generate-tempest-plugins-list.sh`
is using an old flag (`-A`).

This drops the `declare -A plugins` command because `plugins` isn't
used anywhere and also uses `decode('utf-8')` on the initial response
lookup for all the projects which is done already in the script
elsewhere [2].

[0] https://docs.openstack.org/tempest/latest/plugin-registry.html
[1] https://bash.cyberciti.biz/bash-reference-manual/Bash-Builtins.html#index-declare-132
[2] https://github.com/openstack/tempest/blob/da8aec9aedcac940ba1dbc3beee50f05f13af3f1/tools/generate-tempest-plugins-list.py#L67

Change-Id: I70b59c869df06f35c0f7ca6d20e3584502cda8ef
diff --git a/tools/generate-tempest-plugins-list.py b/tools/generate-tempest-plugins-list.py
index 4eb78fb..3772774 100644
--- a/tools/generate-tempest-plugins-list.py
+++ b/tools/generate-tempest-plugins-list.py
@@ -74,7 +74,8 @@
 # Gerrit prepends 4 garbage octets to the JSON, in order to counter
 # cross-site scripting attacks.  Therefore we must discard it so the
 # json library won't choke.
-projects = sorted(filter(is_in_openstack_namespace, json.loads(r.read()[4:])))
+content = r.read().decode('utf-8')[4:]
+projects = sorted(filter(is_in_openstack_namespace, json.loads(content)))
 
 # Retrieve projects having no deb, puppet, ui or spec namespace as those
 # namespaces do not contains tempest plugins.
diff --git a/tools/generate-tempest-plugins-list.sh b/tools/generate-tempest-plugins-list.sh
index b27b23a..111c9ce 100755
--- a/tools/generate-tempest-plugins-list.sh
+++ b/tools/generate-tempest-plugins-list.sh
@@ -41,8 +41,6 @@
 set -ex
 
 (
-declare -A plugins
-
 if [[ -r doc/source/data/tempest-plugins-registry.header ]]; then
     cat doc/source/data/tempest-plugins-registry.header
 fi