BUG: Include find GTest CMake code when installed

Author: blowekamp

Modules/ThirdParty/GoogleTest/CMakeLists.txt

@@ -10,6 +10,10 @@ if(NOT ITK_BINARY_DIR)
   set(GTEST_ROOT \"${GTEST_ROOT}\")
   find_package(GTest REQUIRED)
 endif()
+")
+    set(ITKGoogleTest_EXPORT_CODE_INSTALL "
+  set(GTEST_ROOT \"${GTEST_ROOT}\")
+  find_package(GTest REQUIRED)
 ")
   endif()
 endif ()