services: postgresql: Add postgresql-role-service-type.

* gnu/services/databases.scm (postgresql-role,
postgresql-role?, postgresql-role-name,
postgresql-role-permissions, postgresql-role-create-database?,
postgresql-role-configuration, postgresql-role-configuration?,
postgresql-role-configuration-host, postgresql-role-configuration-roles,
postgresql-role-service-type): New procedures.
* gnu/tests/databases.scm: Test it.
* doc/guix.texi: Document it.

gnu/tests/databases.scm

@@ -217,6 +217,9 @@
 (define %postgresql-log-directory
   "/var/log/postgresql")
 
+(define %role-log-file
+  "/var/log/postgresql_roles.log")
+
 (define %postgresql-os
   (simple-operating-system
    (service postgresql-service-type
@@ -229,7 +232,13 @@
                   ("random_page_cost" 2)
                   ("auto_explain.log_min_duration" "100 ms")
                   ("work_mem" "500 MB")
-                  ("debug_print_plan" #t)))))))))
+                  ("debug_print_plan" #t)))))))
+   (service postgresql-role-service-type
+            (postgresql-role-configuration
+             (roles
+              (list (postgresql-role
+                     (name "root")
+                     (create-database? #t))))))))
 
 (define (run-postgresql-test)
   "Run tests in %POSTGRESQL-OS."
@@ -282,6 +291,39 @@
                   #t))
              marionette))
 
+          (test-assert "database ready"
+            (begin
+              (marionette-eval
+               '(begin
+                  (let loop ((i 10))
+                    (unless (or (zero? i)
+                                (and (file-exists? #$%role-log-file)
+                                     (string-contains
+                                      (call-with-input-file #$%role-log-file
+                                        get-string-all)
+                                      ";\nCREATE DATABASE")))
+                      (sleep 1)
+                      (loop (- i 1)))))
+               marionette)))
+
+          (test-assert "database creation"
+            (marionette-eval
+             '(begin
+                (use-modules (gnu services herd)
+                             (ice-9 popen))
+                (current-output-port
+                 (open-file "/dev/console" "w0"))
+                (let* ((port (open-pipe*
+                              OPEN_READ
+                              #$(file-append postgresql "/bin/psql")
+                              "-tAh" "/var/run/postgresql"
+                              "-c" "SELECT 1 FROM pg_database WHERE
+ datname='root'"))
+                       (output (get-string-all port)))
+                  (close-pipe port)
+                  (string-contains output "1")))
+             marionette))
+
           (test-end)
           (exit (= (test-runner-fail-count (test-runner-current)) 0)))))