Test polling of parent of HEAD commit with and without workspace

More testing of JENKINS-29066

src/test/java/hudson/plugins/git/GitSCMTest.java

@@ -1429,28 +1429,45 @@ public void testPolling_environmentValueInBranchSpec() throws Exception {
    }

    @Issue("JENKINS-29066")
    public void testPolling_parentHead() throws Exception {
    public void baseTestPolling_parentHead(List<GitSCMExtension> extensions) throws Exception {
        // create parameterized project with environment value in branch specification
        FreeStyleProject project = createFreeStyleProject();
        GitSCM scm = new GitSCM(
                createRemoteRepositories(),
                Collections.singletonList(new BranchSpec("**")),
                false, Collections.<SubmoduleConfig>emptyList(),
                null, null,
                Collections.<GitSCMExtension>emptyList());
                extensions);
        project.setScm(scm);

        // commit something in order to create an initial base version in git
        commit("toto/commitFile1", johnDoe, "Commit number 1");
        git.branch("someBranch");
        commit("toto/commitFile2", johnDoe, "Commit number 2");

        assertTrue("polling should detect changes",project.poll(listener).hasChanges());

        // build the project
        build(project, Result.SUCCESS);

        /* Expects 1 build because the build of someBranch incorporates all
         * the changes from the master branch as well as the changes from someBranch.
         */
        assertEquals("Wrong number of builds", 1, project.getBuilds().size());

        assertFalse("polling should not detect changes",project.poll(listener).hasChanges());
    }

    @Issue("JENKINS-29066")
    public void testPolling_parentHead() throws Exception {
        baseTestPolling_parentHead(Collections.<GitSCMExtension>emptyList());
    }

    @Issue("JENKINS-29066")
    public void testPolling_parentHead_DisableRemotePoll() throws Exception {
        baseTestPolling_parentHead(Collections.<GitSCMExtension>singletonList(new DisableRemotePoll()));
    }

    public void testPollingAfterManualBuildWithParametrizedBranchSpec() throws Exception {
        // create parameterized project with environment value in branch specification
        FreeStyleProject project = createFreeStyleProject();