Adding the timeout for the connection on the configuration database.

While accessing the configuration database from multiple session, it
results in to the error - OperationError, because - sqlite locks all the
database, and does not allow to access it simultaneously. We added the
timeout to give some time window for accessing it simultaneously.

web/config.py

@@ -160,6 +160,10 @@ SQLITE_PATH = os.path.join(
     os.path.realpath(os.path.expanduser('~/.pgadmin/')),
     'pgadmin4.db'
     )
+# SQLITE_TIMEOUT will define how long to wait before throwing the error -
+# OperationError due to database lock.
+# (Default: 500 milliseconds)
+SQLITE_TIMEOUT = 500
 
 ##########################################################################
 # Server-side session storage path

web/pgadmin/__init__.py

@@ -169,9 +169,10 @@ def create_app(app_name=config.APP_NAME):
     # Setup authentication
     ##########################################################################
 
-    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///{0}'.format(
-            config.SQLITE_PATH.replace('\\', '/')
-            )
+    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///{0}?timeout={1}'.format(
+        config.SQLITE_PATH.replace('\\', '/'),
+        getattr(config, 'SQLITE_TIMEOUT', 500)
+        )
 
     # Only enable password related functionality in server mode.
     if config.SERVER_MODE is True: