[TOREE-546] Mitigate ZeroMQSocketRunnableSpec hang

[pan3793]

This is the second try to fix the ZeroMQSocketRunnableSpec hang. Unfortunately, the previous try #205 seems not help.

The stacktrace is

[info]   - should set the linger option when provided *** FAILED *** (124 milliseconds)
[info]     java.lang.AssertionError: assertion failed: Runnable is not processing or is closed!
[info]     at scala.Predef$.assert(Predef.scala:223)
[info]     at org.apache.toree.communication.socket.ZeroMQSocketRunnable.close(ZeroMQSocketRunnable.scala:187)
[info]     at org.apache.toree.communication.socket.ZeroMQSocketRunnableSpec.$anonfun$new$12(ZeroMQSocketRunnableSpec.scala:138)
...

This time I follow the guidance of ZMQ.Context#close()'s JavaDoc to set ZMQ_LINGER to 0, hope this help.

Warning

As ZMQ_LINGER defaults to "infinite", by default this method will block indefinitely if there are any pending connects or sends. We strongly recommend to

• set ZMQ_LINGER to zero on all sockets
• close all sockets, before calling this method

[pan3793]

Seems to help but still has a chance to hang, open TOREE-548 to address it in another approach.

Note: this PR does not conflict with TOREE-548, the CI shows it reduces the hang rate compared to the master branch, the reviewer could decide to merge it or ignore it.