Filter out unsupported session types

[rytis]

Right now SparkMagic cannot establish a new connection if there's already a connection of an unsupported kind (for example Zeppelin "shared" session).

This patch is to ignore already established sessions that have unsupported kinds.

[Tagar]

@rytis what currently happens if there is already an established session of type "shared"?

https://github.com/apache/incubator-livy/blob/branch-0.6/core/src/main/scala/org/apache/livy/sessions/Kind.scala#L34

It's an interesting idea for sparkmagic to support shared session across different notebooks. I see so many use cases for this.

Thank you.