Testing/Install: cleanup and include in the new build

Testing/Install/CMakeLists.txt

 # Test "make install"
-if("x${CMAKE_INSTALL_PREFIX}" MATCHES "^x${VTK_BINARY_DIR}/InstallTest$")
-  add_test(NAME Install
-    COMMAND ${CMAKE_COMMAND} -DCONFIGURATION=$<CONFIGURATION>
-                             -DVTK_BINARY_DIR=${VTK_BINARY_DIR}
-                             -P ${CMAKE_CURRENT_SOURCE_DIR}/InstallTest.cmake
-    )
-endif()
+if (CMAKE_INSTALL_PREFIX STREQUAL "${VTK_BINARY_DIR}/InstallTest")
+  add_test(
+    NAME    Install
+    COMMAND "${CMAKE_COMMAND}"
+            -DCONFIGURATION=$<CONFIGURATION>
+            "-DVTK_BINARY_DIR=${VTK_BINARY_DIR}"
+            -P "${CMAKE_CURRENT_SOURCE_DIR}/InstallTest.cmake")
+endif ()

Testing/Install/InstallTest.cmake

-if(NOT DEFINED VTK_BINARY_DIR)
+if (NOT DEFINED VTK_BINARY_DIR)
   message(FATAL_ERROR "Invoke with -DVTK_BINARY_DIR=/path/to/VTK/build")
-endif()
-if(NOT DEFINED CONFIGURATION)
+endif ()
+if (NOT DEFINED CONFIGURATION)
   message(FATAL_ERROR "Invoke with -DCONFIGURATION=<config>")
-endif()
+endif ()
 message(STATUS "Removing InstallTest directory...")
 file(REMOVE_RECURSE "${VTK_BINARY_DIR}/InstallTest")
 message(STATUS "Building 'install' target...")
 execute_process(
-  COMMAND ${CMAKE_COMMAND} --build "${VTK_BINARY_DIR}"
-                           --target install
-                           --config "${CONFIGURATION}"
-  RESULT_VARIABLE failed
-  )
-if(failed)
+  COMMAND "${CMAKE_COMMAND}"
+          --build "${VTK_BINARY_DIR}"
+          --target install
+          --config "${CONFIGURATION}"
+  RESULT_VARIABLE failed)
+
+if (failed)
   message(FATAL_ERROR "Installation failed: ${failed}")
-else()
-  file(WRITE "${VTK_BINARY_DIR}/InstallTest/InstallSucceeded.txt" "# Installation succeeded!\n")
-endif()
+else ()
+  file(WRITE "${VTK_BINARY_DIR}/InstallTest/InstallSucceeded.txt"
+    "# Installation succeeded!\n")
+endif ()