Allow timeouts to be specified on Drydock SSH connections
Summary: This allows timeouts to be specified on SSH connections that Drydock makes. Used in the EC2 allocator to poll for the SSH server starting.
Test Plan: Used in EC2 allocator diff.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D10225