Fix attempt for OperatorPivotTest

[akarnokd]

This is an attempt to fix the lack of concurrency in the OperatorPivotTest.testConcurrencyAndSerialization. Since this fails mostly on the build server, I'll try to minimize the attempts to not flood it.

[cloudbees-pull-request-builder]

RxJava-pull-requests #1103 FAILURE
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[akarnokd]

There is something wrong with JavaFX compilation:

rxjava-contrib/rxjava-javafx/src/main/java/rx/observables/JavaFxObservable.java:19: error: package javafx.beans.value does not exist
import javafx.beans.value.ObservableValue;
                         ^

[benjchristensen]

I have commented out javafx until we resolve the compilation issue.