Fixed the errors, and warnings reported by pylama.

TODO::
- Don't use unicode in Python 3 for removing the support of Python 2 (
  psycopg2 driver - __init__.py, server_manager.py).
- Merge the lastest pgcli (version: 3.0.0) for SQL autocompletion.

web/pgadmin/browser/server_groups/servers/databases/schemas/tables/constraints/foreign_key/__init__.py

@@ -13,7 +13,7 @@ import simplejson as json
 from functools import wraps
 
 import pgadmin.browser.server_groups.servers.databases as database
-from flask import render_template, make_response, request, jsonify
+from flask import render_template, request, jsonify
 from flask_babelex import gettext
 from pgadmin.browser.server_groups.servers.databases.schemas.tables.\
     constraints.type import ConstraintRegistry, ConstraintTypeModule
@@ -517,7 +517,7 @@ class ForeignKeyConstraintView(PGChildNodeView):
                 return make_json_response(
                     status=400,
                     success=0,
-                    errormsg=_(
+                    errormsg=gettext(
                         "Could not find required parameter ({})."
                     ).format(arg)
                 )
@@ -525,7 +525,7 @@ class ForeignKeyConstraintView(PGChildNodeView):
                 return make_json_response(
                     status=400,
                     success=0,
-                    errormsg=_(
+                    errormsg=gettext(
                         "Could not find required parameter ({})."
                     ).format(arg)
                 )

web/pgadmin/browser/server_groups/servers/databases/schemas/tables/templates/foreign_key/sql/tests/test_foreign_key_properties.py

@@ -11,10 +11,11 @@ import os
 from pgadmin.utils.driver import DriverRegistry
 from regression.python_test_utils.template_helper import file_as_template
 
-DriverRegistry.load_drivers()
 from pgadmin.utils.route import BaseTestGenerator
 from regression.python_test_utils import test_utils
 
+DriverRegistry.load_drivers()
+
 
 class TestColumnForeignKeyGetConstraintCols(BaseTestGenerator):
     scenarios = [