ttrss: Ensure database used is PostgreSQL

- Installing dbcommon-pgsql and not install dbcommon-mysql does not
  ensure that PostgreSQL is selected as the database for the
  application.  Set a debconf value to force selection of PostgreSQL.

- Minor styling fixes.

actions/ttrss

@@ -23,6 +23,7 @@ Configuration helper for Tiny Tiny RSS.
 
 import argparse
 import augeas
+import subprocess
 
 from plinth import action_utils
 
@@ -35,6 +36,7 @@ def parse_arguments():
     parser = argparse.ArgumentParser()
     subparsers = parser.add_subparsers(dest='subcommand', help='Sub command')
 
+    subparsers.add_parser('pre-setup', help='Perform pre-setup operations')
     subparsers.add_parser('setup', help='Setup Tiny Tiny RSS configuration')
     subparsers.add_parser('enable', help='Enable Tiny Tiny RSS site')
     subparsers.add_parser('disable', help='Disable Tiny Tiny RSS site')
@@ -42,6 +44,13 @@ def parse_arguments():
     return parser.parse_args()
 
 
+def subcommand_pre_setup(_):
+    """Preseed debconf values before packages are installed."""
+    subprocess.check_output(
+        ['debconf-set-selections'],
+        input=b'tt-rss tt-rss/database-type string pgsql')
+
+
 def subcommand_setup(_):
     """Setup Tiny Tiny RSS configuration."""
     aug = load_augeas()

plinth/modules/ttrss/__init__.py

@@ -58,6 +58,7 @@ def init():
 
 def setup(helper, old_version=None):
     """Install and configure the module."""
+    helper.call('pre', actions.superuser_run, 'ttrss', ['pre-setup'])
     helper.install(['tt-rss', 'postgresql', 'dbconfig-pgsql', 'php-pgsql'])
     helper.call('post', actions.superuser_run, 'ttrss', ['setup'])
     helper.call('post', service.notify_enabled, None, True)
@@ -72,7 +73,7 @@ def get_status():
 def is_enabled():
     """Return whether the module is enabled."""
     return (action_utils.service_is_enabled('tt-rss') and
-                action_utils.webserver_is_enabled('tt-rss-plinth'))
+            action_utils.webserver_is_enabled('tt-rss-plinth'))
 
 
 def is_running():

plinth/modules/ttrss/urls.py

@@ -16,7 +16,7 @@
 #
 
 """
-URLs for the ttrss module.
+URLs for the Tiny Tiny RSS module.
 """
 
 from django.conf.urls import url