DuneModuleDependencies.cmake warning about dune-uggrid.

After !1249 (merged) was merged I now get the following warning, since I don't have dune-uggrid installed:

--   Package 'dune-uggrid' not found
CMake Warning at dune-common/cmake/modules/DuneModuleDependencies.cmake:241 (find_package):
  By not providing "Finddune-uggrid.cmake" in CMAKE_MODULE_PATH this project
  has asked CMake to find a package configuration file provided by
  "dune-uggrid", but CMake did not find one.

  Could not find a package configuration file provided by "dune-uggrid" with
  any of the following names:

    dune-uggridConfig.cmake
    dune-uggrid-config.cmake

  Add the installation prefix of "dune-uggrid" to CMAKE_PREFIX_PATH or set
  "dune-uggrid_DIR" to a directory containing one of the above files.  If
  "dune-uggrid" provides a separate development package or SDK, be sure it
  has been installed.
Call Stack (most recent call first):
  dune-common/cmake/modules/DuneModuleDependencies.cmake:324 (find_dune_package)
  dune-common/cmake/modules/DuneModuleDependencies.cmake:377 (dune_process_dependency_leafs)
  dune-common/cmake/modules/DuneModuleDependencies.cmake:384 (dune_create_dependency_leafs)
  dune-common/cmake/modules/DuneModuleDependencies.cmake:384 (dune_create_dependency_leafs)
  dune-common/cmake/modules/DuneModuleDependencies.cmake:384 (dune_create_dependency_leafs)
  dune-common/cmake/modules/DuneModuleDependencies.cmake:136 (dune_create_dependency_leafs)
  dune-common/cmake/modules/DuneProject.cmake:121 (dune_create_dependency_tree)
  CMakeLists.txt:18 (dune_project)

@santiago.ospina: Could you please look into this and fix it.