remove the pip install tensorboard

[kkasravi]

/assign @jlewi

This is for the issue #428 "remove tensorboard link from jupyter" and #297 "add prototypes for TensorBoard". In general we're utilizing the ksonnet way to launch tensorboard rather than using a button in jupyterhub.

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This change is 

[kkasravi]

this is a screen shot from a container i built for tensorflow-notebook-cpu and uploaded to hub.docker.com https://hub.docker.com/r/nervana/tensorflow-notebook-cpu/tags/

[kkasravi]

/test

[jlewi]

Thanks for this.

Could you update the PR description to explain why we ware making this change and link to the relevant issues? i.e. #428 to remove the link and #297 to add prototypes for TensorBoard.

[jlewi]

@pdmack I think you helped a customer recently get this working. Any reason we should keep this rather than telling customers to directly launch TB and potentially providing a UI for that if we think one is needed?

[kkasravi]

@jlewi updated the PR description

[kkasravi]

/retest

[jlewi]

/approve

[jlewi]

/lgtm

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[pdmack]

@jlewi Sorry, too slow. I think clear instructions for accessing TB will be fine. The user wasn't aware that the menu item was there, and therefore tried to launch it from the NB terminal. Also, they were using a spawned image which had TB launch issues (even from the menu).