Optimize default VM management to avoid unnecessary project updates

[fbricon]

With the previous code, the java.home was initially prepared to be used as default VM, even though there was a default runtime set, potentially triggering unnecessary full builds

[fbricon]

this caused full builds even though there was already a default runtime environment

[snjeza]

@fbricon could you try to apply the following patch:

diff --git a/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/managers/GradleProjectImporter.java b/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/managers/GradleProjectImporter.java
index 2909c4bf..fa1087fb 100644
--- a/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/managers/GradleProjectImporter.java
+++ b/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/managers/GradleProjectImporter.java
@@ -276,7 +276,7 @@ public class GradleProjectImporter extends AbstractProjectImporter {
        }
 
        private static boolean checkGradlePersistence(boolean shouldSynchronize, IProject project, File projectDir) {
-               if (!ProjectUtils.isJavaProject(project) || !project.getFile(IJavaProject.CLASSPATH_FILE_NAME).exists()) {
+               if (ProjectUtils.isJavaProject(project) && !project.getFile(IJavaProject.CLASSPATH_FILE_NAME).exists()) {
                        return true;
                }
                PersistentModel model = CorePlugin.modelPersistence().loadModel(project);