utils: add struct test_suite

utils: add struct test_suite

Provide a convenient wrapper struct which provides the tests and the
number of tests. The struct can be kept local to each source file so we
are sure that the tests and number of tests is correct.

In vfstest.c we provide a run_suite() function which expects a struct
test_suite and runs the tests provided by that suite.

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>