Cleanup zookeeper integration testing

In the persistence tests only use zake when zookeeper is
not available (and of the right version). When zookeeper is
available skip running zake.

In the jobboard tests split out the tests which are not
specific for zake into a base class (allowing for a future
commit to add a zookeeper integration test).

Change-Id: I50d51639a7f6c03c29d559c485676fddb9a7cf20
Merge "Cleanup zookeeper integration testing"