Fixed path for rzeppelin package for some users. [ZEPPELIN-810] Revise R Tutorial notebook [ZEPPELIN-811]

[elbamos]

What is this PR for?

1. Fix a bug reported by J. Muedsam, where if Zeppelin is launched from a working directory that isn't the ZEPPELIN_HOME, it could fail to find the rzeppelin R package.
2. Fixes to the R tutorial notebook.

What type of PR is it?

[Bug Fix | Documentation]

Todos

What is the Jira issue?

https://issues.apache.org/jira/browse/ZEPPELIN-810
https://issues.apache.org/jira/browse/ZEPPELIN-811

How should this be tested?

The existing unit and integration tests should handle 810.
For 811, try the notebook.

Screenshots (if appropriate)

Questions:

• Does the licenses files need update? No.
• Is there breaking changes for older versions? No.
• Does this needs documentation? No.

[jeffsteinmetz]

It's hard to tell what has changed in notebook/r/note.json, perhaps it could be its own PR and limit this PR to Fixed path for rzeppelin package?
There are 155 additions, 298 deletions to note.json

[bzz]

Not sure if it is ready for review yet, but I second @jeffsteinmetz on preferably having 2 separate PRs.