bug: Image get endpoint doesn't work when image name contains `/`

[VoVAllen]

Description

We used authorized.GET("/:login_name/images/:name", WrapHandler(s.imageGet)) to register the imageGet handler. However, it's common for image name to be nvidia/cuda, which cannot be properly matched with /:name.

Note other restful API may also have similar problems, such as special characters in environment name or username.

cc @gaocegege

Reproduction

Additional Info

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[gaocegege]

I think we have a escape here

/cc @kemingy

[VoVAllen]

Not sure what's the best practice here. It's not common to escape / in the URL. Ref: https://stackoverflow.com/questions/48186760/rest-url-parameter-with-slashes#comment83377972_48193355

[gaocegege]

Actually we should use digest, I think.