Bump up default timeout for waiting for gRPC server
Summary: 3 seconds is quite aggressive for a process that can involve loading user code (and is manifesting as such in flaky tests on Windows). Bump up to 15 seconds.
Test Plan: BK + Azure
Reviewers: alangenfeld, max, sashank
Reviewed By: alangenfeld
Differential Revision: https://dagster.phacility.com/D4906