The commit "Fake $HOME to isolate tests from user" started setting $HOME
in the CTest script environment.  On some platforms tests depend on some
local configuration in the home directory, such as the "cvs login" for
KWSys in CTestTest3.

In this commit we now construct a fake home dir during CMake config step
and populate it with a .cvspass file needed by the test.  We also check
CTEST_NO_TEST_HOME to optionally disable the test home.

See issue #9949.