r/postgresql-server-base: Factor out prep steps

There's a bit of a dependency loop between the _postgresql-server_ role
and other roles that supplement it, like _wal-g-pg_ and
_postgresql-cert_.  The latter roles need PostgreSQL installed, but when
those roles are used, the server cannot be started until they have been
applied.  To resolve this situation, I've broken out the initial
installation steps from the _postgresql-server_ role into
_postgresql-server-base_.  Roles that need PostgreSQL installed, but
need to be applied before the server can start, can depend on this role.

roles/postgresql-cert/meta/main.yml

@@ -0,0 +1,3 @@
+dependencies:
+- systemd-base
+- postgresql-server-base

roles/postgresql-cert/tasks/main.yml

@@ -2,7 +2,6 @@
   package:
     name:
     - certbot
-    - postgresql-server  # to get postgres user account
     state: present
   tags:
   - install

roles/postgresql-server-base/tasks/main.yml

@@ -0,0 +1,38 @@
+- name: ensure postgresql-server is installed
+  package:
+    name:
+    - postgresql-server
+    - postgresql-upgrade
+    state: present
+  tags:
+  - install
+
+- name: ensure postgresql-upgrade script is installed
+  copy:
+    src: postgresql-upgrade.sh
+    dest: /usr/local/libexec/postgresql-upgrade
+    owner: root
+    group: root
+    mode: u=rwx,go=rx
+  tags:
+  - postgresql-upgrade
+- name: ensure postgresql-upgrade systemd unit is installed
+  copy:
+    src: postgresql-upgrade.service
+    dest: /etc/systemd/system/postgresql-upgrade.service
+    owner: root
+    group: root
+    mode: u=rw,go=r
+  notify:
+  - reload systemd
+  tags:
+  - postgresql-upgrade
+  - systemd
+
+- name: ensure postgresql-upgrade service starts when needed
+  service:
+    name: postgresql-upgrade
+    enabled: true
+  tags:
+  - postgresql-upgrade
+  - service

roles/postgresql-server/meta/main.yml

@@ -1,2 +1,3 @@
 dependencies:
 - systemd-base
+- postgresql-server-base

roles/postgresql-server/tasks/main.yml

@@ -1,12 +1,3 @@
-- name: ensure postgresql-server is installed
-  package:
-    name:
-    - postgresql-server
-    - postgresql-upgrade
-    state: present
-  tags:
-  - install
-
 - name: restore postgresql data directory from backup
   command: >-
     {{ postgresql_restore_command }}
@@ -132,35 +123,6 @@
   tags:
   - systemd
 
-- name: ensure postgresql-upgrade script is installed
-  copy:
-    src: postgresql-upgrade.sh
-    dest: /usr/local/libexec/postgresql-upgrade
-    owner: root
-    group: root
-    mode: u=rwx,go=rx
-  tags:
-  - postgresql-upgrade
-- name: ensure postgresql-upgrade systemd unit is installed
-  copy:
-    src: postgresql-upgrade.service
-    dest: /etc/systemd/system/postgresql-upgrade.service
-    owner: root
-    group: root
-    mode: u=rw,go=r
-  notify:
-  - reload systemd
-  tags:
-  - postgresql-upgrade
-  - systemd
-
-- name: ensure postgresql-upgrade service starts when needed
-  service:
-    name: postgresql-upgrade
-    enabled: true
-  tags:
-  - postgresql-upgrade
-  - service
 - name: ensure postgresql starts at boot
   service:
     name: postgresql