Tweak find_package test to turn off as much searching of the host
environment as possible. This should make the tests less likely to be
affected in case the host system happens to have a package with the same
name as one of the test packages.
We are working on adding CPS support to find_package, which will
obviously require tests (ideally, and especially in the long term, a
non-trivial number thereof). While it would be possibly to lump these
into the already rather lengthy FindPackageTest, it seems likely they
can be kept separate. Therefore, rename FindPackageTest to
FindPackageCMakeTest so that the name FindPackageCpsTest will be
available.
