Allow building a client without connecting it immediately

Currently the only way to get a NuxeoClient is to build it with the help of the NuxeoClient.Builder. The final step is to call the method connect and to get the NuxeoClient to use.

This could be a problem for some authentication methods because the connect method leverages /nuxeo/api/v1/automation/login which can have a different authentication chain then the other REST endpoints.

We want to have a build method which will just build the client and return it without performing any check like connect does.