Extend studyjob client API

[andreyvelich]

I added namespace parameter to studyJob client API functions.
After this we can use the API not only inside containers.

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This change is 

[andreyvelich]

@YujiOshima

[hougangliu]

Suggest change namespace == nil to len(namespace) == 0 to handle namespace := []string{};GetWorkerTemplates(namespace...) case

[andreyvelich]

@hougangliu I agree, changed it.

[YujiOshima]

@andreyvelich Thank you. Could you split getting namespace process to another function like func (s *StudyjobClient)getNameSpace(string ns) string?

[andreyvelich]

@YujiOshima Done

[johnugeorge]

@andreyvelich What would be the scenario for multiple namespaces in the function call?

[andreyvelich]

@johnugeorge This is not for multiple scenario, you can run these functions without namespace, if you can take namespace from container.
For example:
list := GetStudyJobList()
or
list := GetStudyJobList(namespace)

[YujiOshima]

@andreyvelich Great! Thanks!
/lgtm

[YujiOshima]

/approve

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