test: only close SSH session if context is canceled
test: only close SSH session if context is canceled

If an SSH has `Run` called on it, and `Run` returns, there is no need to close=
the session because calling `Run` implicitly closes it. If we call `Close` on a
session for which `Run` has already completed, we riddle the logs for test runs
with errors like the following:

```
"failed to close session" error=EOF
```

So, only try to close the session in the case that `session.Run` is still
ongoing (e.g., when a context associated with running the command is canceled /
has reached its timeout).

Signed-off by: Ian Vernon <ian@cilium.io>

cilium/cilium,cilium/cilium,cilium-team/cilium,michi-covalent/cilium,tklauser/cilium,tklauser/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium,cilium/cilium,tgraf/cilium,tklauser/cilium,tgraf/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,tgraf/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium,cilium-team/cilium,michi-covalent/cilium,tgraf/cilium