ansible: Split installation of Go from other dependencies

This makes it easier to skip, if Go has been installed by other means.

scripts/ansible/roles/ava-base/tasks/main.yml

@@ -1,4 +1,4 @@
-- name: Install deps
+- name: Install AVA dependencies
   become: true
   apt:
     name:
@@ -6,7 +6,6 @@
       - cmake
       - curl
       - g++
-      - golang-go  # Assumes Ubuntu 20.04, where this installs Go 1.13
       - libssl-dev
       - libuv1-dev
       - make

scripts/ansible/roles/golang-base/tasks/main.yml

@@ -0,0 +1,9 @@
+- name: Install Go
+  become: true
+  apt:
+    name:
+      # AVA (in May 2020) requires Go 1.13. On Ubuntu 20.04 LTS this package,
+      # provides the appropriate version.
+      - golang-go
+  tags:
+    - golang-base

scripts/ansible/service_playbook.yml

@@ -3,8 +3,9 @@
 - name: Configure AVA service
   hosts: ava_nodes
   roles:
-    - name: ava-base
+    - name: golang-base
     - name: gopath
+    - name: ava-base
     - name: ava-build
     - name: ava-user
     - name: ava-install