test: Robustify TestReauthorize.testSudo
test: Robustify TestReauthorize.testSudo

Create a new user `barney` instead of our over-used `user` name.
Apparently some tests leave behind a valid sudo token in the right
circumstances, which makes the test unexpectedly get sudo privileges at
the beginning.

martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit