add timeout netcat processes

[rcooke-warwick]

This is an attempted fix for the following problem:

• most tests are failing with the latest meta-balena unmanaged test suite at the final test
• the connection seems to just timeout - when looking at a device in the stuck state I saw thousands of stale socat+ssh processes
• I added a timeout to the command to close these after they've been open a long time

Seems to fix the problem - not a great fix but all tests are blocked at the moment

Change-type: patch

[acostach]

lgtm