fix(unlocking agents): discarding stderr

[aminbenmansour]

unlocking agent is done successfully despite throwing errors that prevent the rest of the commands to run

[aminbenmansour]

The script keeps logging the stderr in an endless loop so the next commands are not executed.

At the beginning, I thought keripy dropped support for Mark I agent as the agenting tests are failing but requests on Postman were working seamlessly so I redirect the stderr for /dev/null and the problem was resolved.