Create a new top-level directory called test-data, which will carry
all the test data which is large and/or shared between multiple tests.
There are actually several new subdirectories created:
test-data/binaries: The pre-built binary and library files for random
architectures that we use to test various architecture detection
features (was part of tests/data).
test-data/blank-disks: The blank disks which are used for disk format
detection (was part of tests/data).
test-data/files: Other miscellaneous test files from tests/data that
are not included in the above.
test-data/phony-guests: The phony guests (was tests/guests).
test-data: The top-level directory builds the 'test.iso' image file
that is used for testing the C API and in miscellaneous other tests.
