[refactor] move related packages out of pkg

[allencloud]

Ⅰ. Issue Description

When I am learning the structure of package pkg, I find that there are at least three packages which should be moved out of it:

• client
• quota
• runconfig

Here is my reason:
we usually keep totally general packages in package pkg, while three packages above are something specific, client is for control server or something like that, quota for filesystem quota for container, and runconfig is for pouch container's some kind of config parameter.

I wish we could add a folder which is named storage, then some structure may be like:

storage:
     \___volume
      \__quota
       \_ controlserver
                 \_client

Actually I am afraid the package name of client is not my dishes. Like the code makes me feel confused:

return client.JoinURL(c.BaseURL, types.APIVersion, client.StoragePath)

Here, I think client is a struct instance, however it is a package. So hard to understand and quite awkward.

[allencloud]

discussed with @rudyfly and @HusterWan offline. Also sponsor the point of view above.