[proposal]make default registry more standard

[Ace-Tang]

Ⅰ. Issue Description

flagSet.StringVar(&cfg.DefaultRegistry, "default-registry", "registry.hub.docker.com/library/", "Default Image Registry")

library determine which namespace you want to pull image in a defined registry, it should not in default-registry.

What do you think.

Ⅱ. Describe what happened

Ⅲ. Describe what you expected to happen

Ⅳ. How to reproduce it (as minimally and precisely as possible)

Ⅴ. Anything else we need to know?

Ⅵ. Environment:

• pouch version (use pouch version):
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others:

[allencloud]

Yes, I totally agree with you. @Ace-Tang

[Ace-Tang]

@allencloud , do you have plan to update this.