fix(client): skip logout if connection fails

Logout should never really fail - if the controller is inaccessible, we
should make sure we're deleting the cookies and then return.
Merge pull request #1447 from deis/1053-auth-logout

fix(client): skip logout if connection fails
fix(client): make --auth optional

If --auth was not supplied previously, the code for clusters:update
would break because it was supplied a NoneType when opening the file.
Skipping the code block when --auth is not supplied fixes this issue.
Merge pull request #1456 from deis/1454-fix-auth-option

fix(client): make --auth optional
feat(client): allow cluster id renames