Use "cmake --build" to drive the "install" target from the CMake build
tree itself. This avoids using the heavier "ctest --build-and-test"
just to run the native build tool to drive installation.
We create option CMake_TEST_INSTALL to enable a new CMake.Install test.
It tests running the "make install" target to install CMake itself into
a test directory. We enable the option by default for dashboard builds.