Add retry wrappers to http operations

[TigerCodeHub]

Motivation

• Reduce transient failures from appserver HTTP requests by adding retries to HTTP appserver operations, such as updating nginx config, etc.

Description

• Add a retry_appserver_request generator helper and used AppserverRequestError over AppserverProtocolError (request error includes timeouts and other things) for broader error handling.
• Replace direct appserver_open_http_request calls with yield from retry_appserver_request(...) in Nginx, Docker service, Docker image removal, and database create/delete/password-update paths.
• Increase timeouts for Nginx-related operations to 120 seconds and database operations to 90 seconds where wrapped.