Tests: Remove PowerMock usage

I create this issue to gather ideas to get rid of it.
see https://github.com/jbosstools/jbosstools-openshift/blob/cf544dbec4baa87c63768c43680f0d2d0de2af61/tests/org.jboss.tools.openshift.test/src/org/jboss/tools/openshift/test/core/server/OpenShiftServerUtilsPowerMockTest.java

from why i understand, PowerMock is used only to mock a singleton access in a static method.

The reasonable seems to avoid static method: OpenShiftServerUtils. If we are using an instanciation for this class, then, the call to create the Watcher can be extracted in a method and this method would be classically mockable with Mockito.