Disable running playbooks in serial by default

Run playbooks in serial are unnecessary and may cause some issue. This
patch disables serial.

This patch also removes the serial for MariaDB playbook. MariaDB handle
this internally.

Partial-Bug: #1668185
Change-Id: I3b4216dd82607475e9bd9b44590b631be4abdbdd

ansible/site.yml

@@ -123,7 +123,6 @@
 
 - name: Apply role mariadb
   hosts: mariadb
-  serial: '{{ serial|default("0") }}'
   roles:
     - { role: mariadb,
         tags: mariadb,

releasenotes/notes/disable-serial-in-default-442093aca22658f4.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - Run ansible playbooks in serial is disabled by default now. Serial is not
+    recommended. But you can enable it by configuring ANSIBLE_SERIAL
+    environment variable.

tools/kolla-ansible

@@ -78,6 +78,9 @@ CONFIG_DIR="/etc/kolla"
 PASSWORDS_FILE="${CONFIG_DIR}/passwords.yml"
 DANGER_CONFIRM=
 INCLUDE_IMAGES=
+# Serial is not recommended and disable in default. User could enable it by
+# simple configure ANSIBLE_SERIAL variable
+ANSIBLE_SERIAL=${ANSIBLE_SERIAL:-0}
 
 while [ "$#" -gt 0 ]; do
     case "$1" in
@@ -205,11 +208,11 @@ EOF
         ;;
 (upgrade)
         ACTION="Upgrading OpenStack Environment"
-        EXTRA_OPTS="$EXTRA_OPTS -e action=upgrade -e serial=30%"
+        EXTRA_OPTS="$EXTRA_OPTS -e action=upgrade -e serial=${ANSIBLE_SERIAL}"
         ;;
 (reconfigure)
         ACTION="Reconfigure OpenStack service"
-        EXTRA_OPTS="$EXTRA_OPTS -e action=reconfigure -e serial=30%"
+        EXTRA_OPTS="$EXTRA_OPTS -e action=reconfigure -e serial=${ANSIBLE_SERIAL}"
         ;;
 (stop)
         ACTION="Stop Kolla containers"