tsh logout

[klizhentas]

Logout

# In case if user is logged in as `bob@example.com`, but current shell username is `bob`,
# this will be effect
tsh logout
bob is not logged in

Instead, tsh logout should just clean up all ~/tsh folder basically logging user out at all times.

[kontsevoy]

regression: tsh logout does not remove certs from the SSH agent. when testing this, please make sure it handles --proxy flag properly