Allow custom Interaction/Widgets test timeouts

Create VTK_TEST_TIMEOUT_<test> settings that can be configured
locally to increase the default timeout for tests:

  TerrainPolylineEditor
  TestPickingManagerSeedWidget

Use the existing test timeouts as the default values.

Change-Id: I827078610fff305d24f690f7a278a6503ef32daa
Merge topic 'custom-interaction-test-timeouts' into master

622d753a Allow custom Interaction/Widgets test timeouts