Change register fail message when a user already registered the machine

[niryariv]

In this situation:

ubuntu@gitbucket:~$ hossted register
Email: nir@linnovate.net
Registering user. Please wait a second.
Empty Session Token. Some kind of error occoured - {"msg":"This instance has already been registered under a different owner.","jwt":null,"url":"https://app.hossted.com","success":false}.

Display:
Instance is already registered to another owner. Please contact support@hossted.com if you'd like to add a user

[billylkc]

Should be implemented in v0.1.8

[billylkc]

Implemented in 0.1.8, please check

[niryariv]

Confirmed to work on v0.1.8.

Please modify text to "Instance is already registered. Please contact support@hossted.com if you'd like to add a user" - so the message is correct also in cases when the user runs hossted register again under the same user

[niryariv]

fixed daab39e