postgres: keep root ownership of /var/lib/postgres

Adapt upgrade_pg.sh to avoid manipulating /var/lib/postgres' structure
as the postgres user. Instead, create a new empty data directory owned
by postgres for initdb to use.

roles/postgres/files/upgrade_pg.sh

@@ -30,6 +30,8 @@ if [[ -d /var/lib/postgres/data-$FROM_VERSION ]]; then
 	exit 3
 fi
 
+pacman -S --needed postgresql-old-upgrade
+
 # mask postgresql.service to make sure that other services with
 # Wants=postgresql.service and Restart=on-failure will not start
 # it again during the upgrade
@@ -37,11 +39,12 @@ systemctl mask postgresql.service
 systemctl daemon-reload
 systemctl stop postgresql.service
 
-pacman -S --needed postgresql-old-upgrade
-chown postgres:postgres /var/lib/postgres/
-su - postgres -c "mv /var/lib/postgres/data /var/lib/postgres/data-$FROM_VERSION"
-su - postgres -c 'mkdir /var/lib/postgres/data'
-su - postgres -c 'chattr -f +C /var/lib/postgres/data' || :
+# rename the old cluster and create a new empty 'data' directory for initdb
+mv /var/lib/postgres/{data,data-$FROM_VERSION}
+mkdir /var/lib/postgres/data
+chown postgres: /var/lib/postgres/data
+chattr -f +C /var/lib/postgres/data || :
+
 su - postgres -c 'initdb --locale en_US.UTF-8 -E UTF8 -D /var/lib/postgres/data'
 vimdiff /var/lib/postgres/{data,data-$FROM_VERSION}/pg_hba.conf
 vimdiff /var/lib/postgres/{data,data-$FROM_VERSION}/postgresql.conf
@@ -53,7 +56,9 @@ for f in {fullchain,chain,privkey}.pem; do
 	fi
 done
 
-su - postgres -c "pg_upgrade -b /opt/pgsql-$FROM_VERSION/bin/ -B /usr/bin/ \
+# running pg_upgrade from /tmp so it can create pg_upgrade_internal.log
+su - postgres -c "cd /tmp && \
+	pg_upgrade -b /opt/pgsql-$FROM_VERSION/bin/ -B /usr/bin/ \
 	-d /var/lib/postgres/data-$FROM_VERSION -D /var/lib/postgres/data"
 
 # unmask and start postgresql.service