Since 9694d4a, command.run defaults to an empty environment. This means any sub-process commands spawn children that don't have knowledge of or access to SSH_AUTH_SOCK or SSH_AGENT_PID. The SSH master/first process works because it inherits from the environment but after a tmt-reboot the it dies and new SSH processes can't authenticate without the agent/socket.
Since 9694d4a, command.run defaults to an empty environment. This means any sub-process commands spawn children that don't have knowledge of or access to SSH_AUTH_SOCK or SSH_AGENT_PID. The SSH master/first process works because it inherits from the environment but after a tmt-reboot the it dies and new SSH processes can't authenticate without the agent/socket.