code: public static InstallKernel getInstance(File installRoot) {
          if (installKernel == null) {
              installKernel = new InstallKernelImpl(installRoot);
          }
          return installKernel;
      }
docs: Return the singleton instance of InstallKernel.
  The instance will be reset if the installRoot is changed.
  
  @param installRoot the liberty installation root.
  @return the installKernel