Update the registry client to support pulling public images from docker hub without login
Update the registry client to support pulling public images from docker hub without login

Only add the authentication info when the username is provided to support pulling public images from docker hub without login

Signed-off-by: Wenkai Yin <f217e32b30716cdf38664c331b6ddefbd7f5cdf6@vmware.com>

reasonerjt/harbor,wy65701436/harbor,wy65701436/harbor,wy65701436/harbor,steven-zou/harbor,reasonerjt/harbor,reasonerjt/harbor,steven-zou/harbor,steven-zou/harbor,reasonerjt/harbor,steven-zou/harbor,steven-zou/harbor,wy65701436/harbor,reasonerjt/harbor,wy65701436/harbor,steven-zou/harbor,wy65701436/harbor,reasonerjt/harbor