[easy] Initialize self.client early in ManagedGrpcServerRepositoryLocationHandl…


[easy] Initialize self.client early in ManagedGrpcServerRepositoryLocationHandle so that del won't raise an error if you interrupt a test

Summary: This just eliminates a spammy "No property self.client" defined message if you interrupt a test and it calls del on an object that hasn't been created yet.

Test Plan: BK, run pytest on core_tests and interrupt partway through, no weird "missing property" error messages

Reviewers: alangenfeld, sashank

Reviewed By: sashank

Differential Revision: https://dagster.phacility.com/D5153