Login with leading slash '/' fails

[bupd]

Changes needed

1. Make the login message clean
2. Make the login work even if user gives leading slash for the server address.

❯ harbor login http://registry.bupd.xyz/
Error: login failed, please check your credentials: &{false  0001-01-01T00:00:00.000Z  <nil>  false 0001-01-01T00:00:00.000Z 0 } (*models.UserResp) is not supported by the TextConsumer, can be resolved by supporting TextUnmarshaler interface

[Standing-Man]

This issue is very similar to #271 I am currently working on. I will include this issue in the PR and resolve them together.